From www.bloodjournal.org by guest on June 16, 2017. For personal use only. Blood First Edition Paper, prepublished online September 24, 2015; DOI 10.1182/blood-2015-04-537498 Familial predisposition and genetic risk factors for lymphoma James R. Cerhan1,3 and Susan L. Slager2,3 1 Division of Epidemiology and 2Division of Biomedical Statistics and Informatics, Department of Health Sciences Research; 3Genetic Epidemiology and Risk Assessment Program, Mayo Clinic Comprehensive Cancer Center; Mayo Clinic, Rochester, MN. Correspondence: James Cerhan, Department of Health Sciences Research, Mayo Clinic, 200 First Street SW, Rochester, MN 55905; e-mail: [email protected]. 1 Copyright © 2015 American Society of Hematology From www.bloodjournal.org by guest on June 16, 2017. For personal use only. Abstract Our understanding of familial predisposition to lymphoma (collectively defined as non-Hodgkin lymphoma [NHL], Hodgkin lymphoma [HL], and chronic lymphocytic leukemia [CLL]) outside of rare hereditary syndromes has progressed rapidly during the last decade. First-degree relatives of NHL, HL and CLL patients have an approximately 1.7-fold, 3.1-fold, and 8.5-fold elevated risk of developing NHL, HL and CLL, respectively. These familial risks are elevated for multiple lymphoma subtypes and do not appear to be confounded by non-genetic risk factors, suggesting at least some shared genetic etiology across the lymphoma subtypes. However, a family history of a specific subtype is most strongly associated with risk for that subtype, supporting subtype-specific genetic factors. While candidate gene studies have had limited success in identifying susceptibility loci, genome-wide association studies (GWAS) have successfully identified 67 single nucleotide polymorphisms from 41 loci, predominately associated with specific subtypes. In general, these GWAS-discovered loci are common (minor allele frequency >5%), have small effect sizes (odds ratios of 0.60-2.0), and are of largely unknown function. The relatively low incidence of lymphoma, modest familial risk, and the lack of a screening test and associated intervention all argue against active clinical surveillance for lymphoma in affected families at this time. 2 From www.bloodjournal.org by guest on June 16, 2017. For personal use only. Introduction Lymphomas, defined as non-Hodgkin (NHL), Hodgkin (HL), and chronic lymphocytic leukemia/small lymphocytic lymphoma (herein CLL), are the most common hematologic malignancies in western countries, and combined there are an estimated 95,520 newly diagnosed cases each year in the United States.1 While there has been a long history of case reports of familial clustering of lymphomas and leukemias, it has only been relatively recently that these malignancies were considered to have an important inherited genetic component outside of very rare hereditary cancer syndromes.2 In 2001, the World Health Organization (WHO) introduced an updated classification system for lymphomas based on the REAL classification,3 which became the international gold-standard.4 This classification provided the first biologically based, integrated framework for consistently defining lymphoma subtypes, thereby greatly facilitating research on this heterogeneous group of diseases. Building from prior reviews,5-11 we focus on the strongest data addressing familial predisposition (including twin, case-control and registry-based studies) and germline susceptibility loci (including linkage and genetic association studies) for lymphoma, and put these findings into clinical context. One emerging theme on the etiology of lymphoma is that there is both commonality and heterogeneity for risk factors by subtype,12 and thus we consider this issue as well in the context of familial predisposition and genetic risk factors. Evidence for Familial Predisposition Twin Studies If the concordance rate of a phenotype in monozygotic twins (who share all genes) is higher than the concordance rate for dizygotic twins (who share on average half of their genes), then there is evidence for a genetic component. In a study of 44,788 pairs of twins from Scandinavia,13 there was an excess of concordant monozygotic twins compared to dizygotic twins for leukemia, and the heritability was estimated to be 21% (95%CI 0-0.54); these results 3 From www.bloodjournal.org by guest on June 16, 2017. For personal use only. have been attributed to CLL, as acute lymphoblastic and myeloid leukemia have shown minimal evidence of familial clustering.14 There were insufficient cases to estimate heritability for NHL or HL. In a twin study of lymphomas,15 there was a 100-fold higher risk of HL in monozygotic twins of patients with HL compared background rates (SIR=99; 95%CI 48-182), while there was no excess risk in dizygotic twins; in contrast, there was a 23-fold higher risk of NHL in monozygotic twins of patients with NHL and a 14-fold higher risk in dizygotic twins, suggesting a stronger role for shared environment for NHL. Familial aggregation (Table 1) We summarize the strongest results across different study designs that evaluate the extent that family history of lymphoma is associated with risk of developing lymphoma, including casecontrol, cohort and registry-based studies. We note that none of these study designs can definitively establish an inherited genetic contribution to risk of lymphoma as these approaches are unable to distinguish the role of shared genetics from shared environment. Family size itself may also be associated with lymphoma risk, which can introduce bias in estimating the association of familial aggregation with lymphoma risk. Case-Control Studies. In case-control studies, the prevalence of a family history is compared in case patients to that of controls using an odds ratio (OR) to quantify the magnitude of risk. The largest study to date is a pooled analysis of 17,471 NHL cases and 23,096 controls from 20 case-control studies in the International Lymphoma Epidemiology Consortium (InterLymph),12 which found an 1.8-fold increased risk of NHL (OR=1.8, 95%CI 1.5-2.1) for those with a firstdegree (blood) relative with NHL; there was also elevated NHL risk for individuals who reported a first-degree relative with HL (OR=1.7, 95%CI 1.2-2.3) or leukemia (OR=1.5, 95%CI 1.3-1.8), suggesting susceptibility across these lymphomas. 4 From www.bloodjournal.org by guest on June 16, 2017. For personal use only. Further evaluation of NHL subtypes in Table 1 reveals that risk of CLL was only slightly stronger for a family history of leukemia (OR=2.4) than for NHL (OR=1.9). In contrast, risk of diffuse large B-cell (DLBCL) and follicular (FL) lymphoma were more strongly associated with a family history of NHL (ORs 1.8-2.0) than for leukemia (ORs=1.0-1.2), while marginal zone (MZL), mantle cell (MCL) and peripheral T-cell (PTCL) lymphomas showed similar risks for either type of family history (ORs=1.7-2.0). A family history of HL was associated with increased risk of DLBCL (OR=2.1) and MZL (OR=2.7), but was not significantly associated with risk of CLL, FL, lymphoplasmacytic lymphoma/Waldenstroms Macroglobulinemia (LPL/WM), MCL or PTCL, although ORs were above 1.0 for all subtypes except PTCL. In a comprehensive analysis of all subtypes simultaneously, there was no statistically significant heterogeneity across risk of most common NHL subtypes for either a family history of NHL (PHomogeneity=0.52) or HL (PHomogeneity=0.47). In contrast, there was strong evidence for heterogeneity for a family history of leukemia (PHomogeneity=3.9x10-5), with family history of leukemia most strongly associated with risk of CLL, LPL/WM, MCL and PTCL. Of note, the associations for family history of NHL with risk of NHL12 or specific NHL subtypes (e.g., DLBCL,16 FL,17 CLL,18 MZL,19 LPL/WM20 and PTCL21) remained unchanged after adjusting for extensive subtype-specific risk factors, suggesting that the association of family history may be predominately driven by shared genetics over shared environment. While InterLymph did not report pooled results for risk of HL, a large case-control study conducted in Scandinavia22 reported elevated risk of HL with a family history of HL (OR=3.3), NHL (OR=3.3) and CLL (OR=6.3). Some smaller studies have reported larger ORs for risk of HL with a family history of HL. 23,24 These data provide strong evidence for familial predisposition to lymphoma. However, the case-control study design is susceptible to several types of bias, particularly selection and reporting bias. The former bias can occur when there are systematic differences in how cases and controls are enrolled, most commonly due to exclusion of more aggressive cases (who die 5 From www.bloodjournal.org by guest on June 16, 2017. For personal use only. before they can be enrolled into a study) and how controls are selected (i.e., controls who are not representative of the underlying population that generated the cases due to selection factors or participation rates). The main concern with reporting bias is that cases and controls can differentially report a family history. In a study from Scandinavia that compared self-report to cancer registry data,25 specificity of reporting a hematologic malignancy was very high for both cases (98%) and controls (99%), while sensitivity was much lower at 60% for cases and only 38% for controls. This led to inflated odds ratios (up to 30%) based on self-reported family history data. Cohort studies. Prospective cohort studies overcome many of the limitations of case-control studies, but there are few cohorts that have had detailed data on lymphoma in family members or a sufficient number of lymphoma outcomes to assess risk of specific NHL subtypes. In a national cohort study of 3.5 million people in Sweden born 1973-2008, family history of HL in a parent or sibling was associated with an 7.2 and 8.8-fold higher risk of childhood/young adult HL, respectively,26 while another study reported a 6-fold higher risk for siblings.27 In a cohort study of over 120,000 female California teachers,28 a history of lymphoma in a first-degree relative was associated with a 1.7-fold higher risk of B-cell NHL (RR=1.74, 95%CI 1.16-2.60) based on 478 cases; data on risk for NHL subtypes were not available. The latter finding was highly consistent with pooled case-control data (Table 1) and suggests a lack of major biases at least for the overall NHL association. Registry-based studies. Another major approach to evaluate familial aggregation is to link population-based family registry data with cancer registry data to determine the excess risk of cancer in people with a family history of cancer. Advantages of this approach include population-based assessment, which minimizes selection bias and enhances generalizability, and validation of cancer diagnoses through the use of cancer registries, which eliminates 6 From www.bloodjournal.org by guest on June 16, 2017. For personal use only. reporting bias. Based on data from the Utah Population Database and the Utah Cancer Registry,29 the risk of NHL was increased 1.7-fold in first-degree relatives of a proband with NHL (familial RR=1.68, 95%CI 1.04-2.48) and the risk of lymphocytic leukemia was >5-fold in firstdegree relatives of a proband with lymphocytic leukemia (familial RR=5.69, 95%CI 2.58-10.0). In contrast, the risk of HL was only elevated 1.3-fold in first-degree relatives of a HL proband (familial RR=1.27, 95%CI 0.12-3.65), although power for this estimate was low (only 2 exposed cases). Using updated data and a different analytic approach that estimates the Genealogical Index of Familiality,14 excess relatedness was observed for NHL, HL and CLL. For CLL and NHL, but not HL, the excess relatedness was observed for both distant and overall relatedness. Distant relatedness is due to distant relatives and may be interpreted as providing evidence that familial clustering is more likely due to shared genetic versus shared environmental contribution, as the latter would be lower in distant relationships. The most comprehensive data available on familial aggregation by lymphoma subtypes has been published using registry data from Sweden and Denmark (summarized in Table 1). This approach compares the cancer experience in first-degree relatives of lymphoma patients with the cancer experience in relatives of matched population controls. First-degree relatives of HL patients had a 3.1-fold increase in risk of HL (95%CI 1.8-5.3), while risk of HL was not associated with a family history of NHL (RR=1.3, 95%CI 0.9-1.8) but was associated with a family history of CLL (RR=2.1, 95%CI 1.2-3.8).30 In other registry-based studies, risk of HL in first degree relatives of HL patients has ranged from 1.2 to 5.8.31-33 Across studies, risk of HL is stronger for HL in siblings than in parents.26,30-32 First-degree relatives of cases with NHL had a 1.7-fold higher risk of developing NHL (95%CI 1.4-2.2), while risk of NHL was weaker and not statistically significant for first-degree relatives with HL (RR=1.4, 95%CI 1.0-2.0) or CLL (RR=1.3, 95%CI 0.9-1.9).34 First-degree relatives of CLL patients had an 8.5-fold increased risk of CLL (RR=8.5, 95%CI 6.1-12), while risk of CLL was also increased with a first-degree relative with NHL (RR=1.9, 95%CI 1.5-2.3) or 7 From www.bloodjournal.org by guest on June 16, 2017. For personal use only. HL (RR=1.5, 95%CI 1.0-2.3).35 It is notable that most of the risk estimates from the populationbased registry studies in Table 1 were very similar or only modestly weaker than the estimates from the pooled case-control studies, again suggesting that there was only modest bias in estimates from case-control studies. The most prominent exception is for a family history of CLL, which showed a much stronger association in the registry studies compared to that of case-control studies. This may be in part due to the confusion of patients reporting a CLL as a leukemia or lymphoma. The registry studies have also been able to evaluate risk for more detailed lymphoma subtypes. One striking finding is the clustering of risk by NHL subtype. For example, firstdegree relatives of DLBCL cases had a 9.8-fold increased risk of DLBCL,36 first-degree relatives of FL had a 4-fold increased risk of FL,36 and first-degree relatives of LPL/WM had a 20-fold increased risk of LPL/WM.37 In contrast, risk of a different subtype was much weaker, and notably relatives of DLBCL patients were not at increased risk of FL and relatives of FL patients were not at increased risk of DLBCL.36 There are very limited data on PTCL, and registry data suggests no increased risk among first-degree relatives with HL, CLL, DLBCL, or FL.36 Summary. Multiple lines of data suggest that a family history of lymphoma is associated with an increased risk of lymphoma, familial risk is elevated for multiple lymphoma subtypes, and familial risk does not seem to be confounded by non-genetic risk factors, although there are likely unidentified risk factors and clustering of known (and unknown) risk factors within families is difficult to exclude. This suggests at least some shared genetic etiology across the lymphoma subtypes. However, because a family history of a specific lymphoma subtype is also most strongly associated with risk for that specific lymphoma, genetic factors are also likely to be unique to a subtype. Genetic Risk Factors 8 From www.bloodjournal.org by guest on June 16, 2017. For personal use only. We now review studies that show not only clear evidence of a genetic contribution to lymphoma risk, but also provide chromosomal locations that are associated with risk. Linkage Studies Linkage studies use multi-case families or sib pairs to screen the genome in an unbiased manner to identify chromosomal regions that show excessive sharing of inherited alleles among affected individuals. These regions can then be interrogated for causal variants using a variety of approaches, most commonly fine-mapping using dense genotyping or sequencing. The expectation is to identify highly penetrant variants of modest to large effect size, although these variants are generally rare or very rare in the general population. Linkage studies in HL have identified both HLA class I (for EBV+) and class II (for EBV-) risk and protective alleles and haplotypes.10,11 Beyond HLA, linkage studies in CLL,38 HL,39 and WM40 have not definitively identified genes with large effects, and there are no published studies in FL, DLBCL or other NHL subtypes. For CLL, significant linkage was identified at 2q21.2, which contains the chemokine receptor (CXCR4) gene and for which rare coding mutations have been identified.41 The lack of strong findings for these linkage studies may be due to small sample sizes, but also raises the hypothesis that multiple, low to moderate risk variants that are common in the population, defined as minor allele frequency (MAF) >5%, may be more relevant in lymphoma etiology than single, highly penetrant variants that are very rare, which is referred to as the common-disease, common-variant hypothesis.42 Genetic Association Studies With the advent of high-throughput and relatively inexpensive genotyping technologies, casecontrol studies (also commonly called association studies in the genetics literature) of sequence variation in germline DNA have become a predominant study design in genetic epidemiology.43 9 From www.bloodjournal.org by guest on June 16, 2017. For personal use only. This design is a very efficient strategy to identify low penetrance alleles relative to linkage studies, which are underpowered for this task.44 The most common type of genetic variation in the human genome is the single nucleotide polymorphism (SNP), which is a single base pair change in the DNA sequence. In this setting, SNP allele or genotype frequencies in cases (patients) are compared to that in unrelated controls (who do not have the phenotype of interest) using an OR. When the genetic model (e.g., dominant vs. recessive) is not known a priori, the OR is typically modeled as “per risk allele” (i.e., ordinal test of 0, 1 or 2 risk alleles). While other genetic variation is of interest, including rare variants (<5% frequency), insertion/deletions, block substitutions, inversions, translocations and copy number alterations, these have not been studied as extensively.45 Two major types of association studies are candidate gene and genome-wide association studies (GWAS). Candidate Gene Studies The choice of a candidate gene has been mainly driven by a priori biologic knowledge of lymphoma and diseases associated with lymphoma (e.g., infectious or autoimmune), or results identified in other cancers. Candidate gene studies have included pathways related to immune function, cell cycle/proliferation, apoptosis, DNA repair, and carcinogen metabolism. Early studies tended to evaluate a small number of genes (i.e., <5) and were generally restricted to 1 or 2 SNPs within a gene. These SNPs often had some evidence for their functionality based on laboratory data or anticipated changes in protein coding or gene activity (e.g., changes in promotor function). As genotyping technologies increased in throughput and decreased in cost, more SNPs within genes and more genes (often grouped into pathways) were assessed. Also, the International Haplotype Map (“HapMap”)46 and later the 1000 Genomes47 projects, which catalogue human genetic variation, became available as a reference and allowed “tagging” of genes and gene regions to take advantage of linkage disequilibrium (LD) to efficiently cover all of the common genetic variation for more comprehensive genotyping studies.43 10 From www.bloodjournal.org by guest on June 16, 2017. For personal use only. While many studies of candidate genes have been published (reviewed in7-9,11,48), most findings have failed to replicate likely due to study design, bias from population stratification (i.e., confounding by race or ethnicity), small sample size (low power), uncontrolled multiple testing (leading to false positive associations), and unrealistic expectations in our ability to choose variants and genes.49 The most robust findings have been for an LTA-TNF haplotype with DLBCL (P=2.93x10-8);50,51 a SNP (rs3789068) in the proapoptotic BCL2L11 gene and risk for B-cell NHL (OR=1.21, P=2.21x10-11);52 SNPs in CASP8/CASP10 and risk of CLL;53 a SNP (rs3132453) in PRRC2A in HLA class III and risk of B-cell NHL (OR=0.68, P=1.07x10-9);52 and certain HLA alleles in class I (including HLA-A*01 and *02) with EBV+ HL and class II (including HLA-DRB1) with EBV- HL.11 GWAS (Table 2) In contrast to candidate gene/pathway studies, GWA studies use dense microarrays with a large number of SNPs (commonly 250,000 to 750,00 or more) spread across all chromosomes to identify genetic markers associated with case-control status.54 While SNPs on these platforms have generally focused on common variants (MAF≥5%), more recent arrays are enriching for rarer variants (MAF<5%). GWAS is considered agnostic (“hypothesis-free”) as all loci are considered equally. Given the large number of statistical tests involved, a stringent level of evidence (currently P<5 x 10-8) and replication across multiple independent studies are required to declare an association as “genome-wide significant.” An advantage of having a large number of typed SNPs is that any underlying difference in population structure between cases and controls can be identified and controlled to ensure that confounding by race/ethnicity does not bias the results. CLL. The estimated contribution of all common variation to the heritability of CLL is 46-59%.55,56 The first GWAS in a lymphoid malignancy was conducted for CLL57 and to date, GWAS 11 From www.bloodjournal.org by guest on June 16, 2017. For personal use only. analyses55,58-62 have identified 32 SNPs from 28 loci for CLL, which accounts for approximately 19% of familial risk of CLL.61 Many of the established SNPs are near or in genes plausibly linked to CLL, including genes involved in apoptosis (including FAS, PMAIP1, BAK1, BCL2, BCL2L11, BMF, CASP8/CASP10), telomere function (POT1, TERT, TERC), transcription factors important in B-cell differentiation (IRF8, LEF1, PRKD3, SP140), and B-cell receptor activation (IRF3, HLA-DQA1). Notably, there has been little evidence of interaction among these SNPs, suggesting independent effects. None of the SNPs have individually shown a strong relationship with age at diagnosis, although cases diagnosed at a younger age tended to carry a greater number of risk alleles,61 supporting the hypothesis that early onset CLL is enriched for genetic susceptibility. In an East Asian population, GWAS-discovered SNPs for CLL near IRF4 (rs872071), SP140 (rs13397985), and ACOXL (rs17483466) were associated with CLL risk (nominal P<0.05), with a suggestive association with GRAMD1B (rs735665).63 The minor allele frequencies of these SNPs were much lower than in populations of European descent, supporting the hypothesis that the lower prevalence of CLL genetic risk factors might explain part of the lower incidence of CLL in East Asian populations. FL. Three early GWA studies based on small discovery sets (<400 cases) identified loci at 6p21.3364 and 6p21.3265,66 in the major histocompatibility complex (MHC) associated with FL. In a meta-analysis of those studies plus a new GWAS of over 2100 cases, the HLA region showed overwhelming association with FL, with 8,104 SNPs achieving genome-wide significance. A top SNP from this region, rs12195582, reached P=5.35x10-100 after additional validation.67 HLA alleles and amino acids (AA) were imputed and the top signal mapped to four linked DRβ1 multiallelic AA at positions at 11, 13, 28 and 30, suggesting an important role for DRβ1 peptide presentation in FL.67 Additional independent signals were also identified in HLA class II (rs17203612) and class I (rs3130437, near HLA-C); after accounting for all of these 12 From www.bloodjournal.org by guest on June 16, 2017. For personal use only. signals, no other previously identified SNPs from the MHC achieved genome-wide significance. Outside of the HLA region, 5 novel loci have been identified including 11q23.3 (near CXCR5), 11q24.3 (near ETS1), 3q28 (in LPP), 18q21.33 (near BCL2), and 8q24 (near PVT1).67 These genes are linked to B-cell biology making them plausible in the etiology of FL. HL. Classical HL (cHL) makes up approximately 95% of HL, and cHL compromises several subtypes: in young children and older adults, mixed cellularity HL (typically EBV+) predominates, while in adolescents and young adults, nodular sclerosing HL (typically EBV-) predominates.68 Five GWAS analyses have been published in HL69-73, and the strongest findings have been for SNPs mapping to HLA class II69-71 in close proximity to HLA-DRA and HLA-DRB1, regions previously linked to HL by HLA-typing studies.74,75 The 6p21.32 locus marked by rs6903608 (near HLA-DRA), was associated with cHL overall and more specifically to EBV-negative cHL,69,70 early onset70,76 and young adult nodular sclerosing HL71 (largely EBV). Additional GWAS signals at 6p21 have been identified in HLA class I,69 with statistically independent associations for rs2248462 (near MICB) for all cHL (irrespective of EBV status); and rs2734986 (3’ untranslated region of HLA-G and near HLA-A) and rs6904029 (near HCG9) for EBV+ cHL. These results confirm earlier studies linking HLA-A*01 and *02 to EBV+ cHL77-79 and support a role for class I but not class II genes in EBV+ HL. Using SNPs to impute classic HLA alleles, two independent signals in the HLA class II region (rs6903608 and rs2281389) were linked to early onset HL, but no specific classical HLA alleles from this region were significant after conditioning on these two SNPs.76 The class II SNP rs6903608 was estimated to account for ~6% of the familial risk in HL.76 Outside of the MHC region, GWAS-discovered loci for HL include 2p16.170 (near REL), 10p1470 (near GATA3), 8q24.2170 (telomeric to PVT1 and near MYC), 5q3169 (a nonsynonymous SNP in IL13), 3p24.173 (5’ to EOMES), 6q23.373 (intergenic to HBS1L and MYB) and 19p13.372 (in intron 2 of TCF3), with only the 2p16.1 and 5q31 loci showing stronger associations with EBV (negative) status. Genes from these non-HLA regions are involved in 13 From www.bloodjournal.org by guest on June 16, 2017. For personal use only. hematopoiesis and immunoregulation, making them plausible susceptibility loci for cHL. HLA and non-HLA-linked loci appear to be independent, and non-HLA loci were estimated to account for ~7% of the familial risk in HL.73 DLBCL. In a GWAS conducted in an East Asian population, a locus at 3q27 (near BCL6 and LPP) was identified,80 although this could not be replicated in independent studies of East Asian81 or European ancestry.82 In a large GWAS of European ancestry,82 novel loci identified included 6p25.3 (EXOC2), 6p21.33 (HLA-B), 2p23.3 (NCOA1), and 8q24.21 (near PVT1 and MYC); the strongest finding after imputing HLA alleles and amino acids (AA) was with HLAB*08:01, although this could not be statistically distinguished from the HLA-B SNP due to high LD. The latter study also estimated that common SNPs, including but not limited to the GWASdiscovered loci, explained approximately 16% of the variance in DLBCL risk overall. Three of the five 5 GWAS-discovered SNPs for DLBCL in Europeans were significantly associated with DLBCL in an East Asian population,81 including EXOC2 (OR=2.04, P=3.9x1010 ), PVT1 (OR=1.34, P=2.1x10-6), and HLA-B (OR=3.05, P=0.009). Overall, MAFs were similar or only modestly lower in the East Asian population for all SNPs except for one of the 8q24 SNPs, which was much rarer. MZL. The only GWAS of this subtype83 identified two distinct loci at 6p21.32 (intragenic to BTNL2, in HLA class II) and 6p21.33 (HLA-B, in HLA class I); these two loci were in low LD and were statistically independent of each other. There was no strong heterogeneity in these results when stratified on mucosa associated lymphoid tissue (MALT) versus non-MALT (splenic MZL and nodal MZL) subtypes, although this was based on a modest sample size. These loci are also associated with autoimmune diseases and immune response, suggesting shared biologic underpinnings with MZL. 14 From www.bloodjournal.org by guest on June 16, 2017. For personal use only. Lymphoma. Only one GWAS has been conducted based on all lymphomas (including HL, multiple myeloma and T-cell cases) as the outcome in both the discovery and validation stages.84 A SNP at 11q12.1 (near LPXN) was identified, and the associations were consistent across the common subtypes. However, this locus has not been replicated in larger GWAS studies based on specific subtypes. Summary To date, GWAS have successfully identified 67 SNPs from 41 genetic loci, mainly associated with specific subtypes (Figure 1), with only two regions—the HLA region and 8q24—associated with multiple lymphoma subtypes; few candidate gene loci have been replicated by GWAS. As shown in Figure 2, the established loci are common (minor allele frequency >5%) and have small effect sizes, supporting a polygenic model for susceptibility. In contrast to GWAS, candidate gene studies in lymphoma have had only minimal success, similar to other cancers.85 Linkage studies have also not been successful in identifying rare alleles causing Mendelian disease, and the evaluation of low-frequency variants with intermediate effects is still in early research phases for lymphoma, but will be challenged by sample size issues.86 The GWASidentified SNPs that have been identified are largely of unknown function. However, a leading hypothesis related for the mechanistic role of these common SNPs is their effect on gene expression (e.g., through effects on promotors or enhancers), but this effect is difficult to identify given an expected modest impact of these SNPs on gene expression and the fact that this impact could occur at any time before diagnosis.61 Practice Implications Given the estimated lifetime risk of NHL is 1 in 48 (2.1%) in the United States1 and an RR of 1.7 for the risk of NHL in a first-degree relative, then the absolute lifetime risk of NHL is 3.6% in firstdegree relatives of an NHL patient. The absolute risk is even lower for specific lymphoma 15 From www.bloodjournal.org by guest on June 16, 2017. For personal use only. subtypes, which are less common. While the absolute lifetime risk of NHL is not trivial, the relatively low incidence of lymphoma, the modest familial risk, and the lack of a screening test and associated intervention all argue against active clinical surveillance of family members of lymphoma patients at this time. One hope is that genetic risk scores, alone or in combination with other risk factors, might improve prediction ability.87 While there are currently no validated risk scores for lymphoma, this advance is anticipated as more loci are characterized. Future Directions Characterization of genetic susceptibility in lymphoma is rapidly evolving. It is expected that additional common variants will be discovered for the different lymphoma subtypes,88 and perhaps pan-lymphoma loci will also be identified. As new lymphoma entities and precursor lesions are defined, evaluation of heritability and genetic susceptibility should be addressed. Additional work needs to occur in other racial and ethnic groups, particularly with contrasting lymphoma incidence rates. It is not yet clear if rare and low-frequency variants will play a major role in lymphoma susceptibility. This will be challenging to address due to phenotype heterogeneity and the need for large sample sizes for these relatively rare entities, and both family and association study designs along with bioinformatics and laboratory-based studies will all need to be integrated to achieve progress.86 Other genetic mechanisms (e.g., copy number variation), epigenetics and gene-environment interactions are additional frontiers.85 Finally, integrating somatic and germline genomics should provide additional insights into lymphoma etiology and pathogenesis,89 and hopefully provide novel insights into how to prevent and treat this malignancy. 16 From www.bloodjournal.org by guest on June 16, 2017. For personal use only. Acknowledgements This work was supported by the National Cancer Institute grants R01 CA92153, U01 CA118444, and P50 CA97274. We thank Dr. Thomas Habermann for his critical review of the manuscript, Mr. Curtis Olswald for technical assistance, and Ms. Sondra Buehler for editorial assistance. Authorship: J.R.C. and S.L.S. did the background research and wrote the manuscript. Conflict of interest: The authors declare no competing financial interests. 17 From www.bloodjournal.org by guest on June 16, 2017. For personal use only. Bibliography 1. Siegel RL, Miller KD, Jemal A. Cancer statistics, 2015. CA Cancer J Clin. 2015;65(1):5-29. 2. Segel GB, Lichtman MA. Familial (inherited) leukemia, lymphoma, and myeloma: an overview. Blood Cells Mol Dis. 2004;32(1):246-261. 3. Jaffe ES, Harris NL, Stein H, Vardiman JW. World Health Organization Classification of Tumours: Pathology and Genetics, Tumours of Hematopoietic and Lymphoid Tissues. Lyon: IARC Press; 2001. 4. Swerdlow S, Campo E, Harris N. 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Risk* of lymphoma subtypes by family history of selected cancers in first degree relatives Family history of lymphoma subtype in first degree relative Outcome‡ Study Design References HL CLL/Leukemia DLBCL FL LPL/WM 12 1.8 (1.5-2.1) 1.7 (1.4-2.2) 1.7 (1.2-2.3) 1.4 (1.0-2.0) 1.5 (1.3-1.8) 1.3 (0.9-1.9) --- --- --- 12 1.9 (1.4-2.6) 1.9 (1.5-2.3) 1.3 (0.6-2.6) 1.5 (1.0-2.3) 2.4 (1.9-3.1) 8.5 (6.1-12) -1.0 (0.4-2.5) -1.6 (0.9-2.8) -4.0 (2.0-8.2) NHL Case-control Registry Morton et al. (2014) Goldin et al. (2005)34 CLL Case-control Registry Morton et al. (2014) Goldin et al. (2009)35 DLBCL Case-control Registry Morton et al. (2014) Goldin et al. (2009)36 12 1.8 (1.5-2.3) 2.1 (1.4-3.2) 2.4 (P<0.05) 1.2 (0.9-1.5) -9.8 (3.1-31) -no increase† --- FL Case-control Registry Morton et al. (2014)12 Goldin et al. (2009)36 2.0 (1.6-2.5) 1.5 (0.9-2.4) 1.4 (NS) 1.0 (0.7-1.3) 1.8 (1.0-3.3) -no increase† -4.0 (1.6-9.5) --- LPL/WM Case-control Registry Morton et al. (2014) Kristinsson et al. (2008)37 12 1.2 (0.5-2.8) 3.0 (2.0-4.4) 2.2 (0.5-9.4) 0.8 (0.3-2.2) 2.2 (1.2-4.0) 3.4 (1.7-6.6) --- --- -20 (4.1-98) MZL Case-control Morton et al. (2014)12 1.7 (1.1-2.5) 2.7 (1.4-5.5) 1.7 (1.2-2.4) -- -- -- MCL Case-control Morton et al. (2014)12 2.0 (1.1-3.3) 1.5 (0.5-5.0) 2.0 (1.2-3.2) -- -- -- PTCL Case-control Registry Morton et al. (2014)12 Goldin et al. (2009)36 1.7 (0.9-3.1) 0.9 (0.1-4.4) no increase† 1.8 (1.1-3.1) no increase† -no increase† -no increase† --- HL Case-control Registry Chang et al. (2005)22 Goldin et al. (2004, 2009)30,36 3.3 (1.3-8.0) 1.3 (0.9-1.8) 3.3 (0.5-22) 3.1 (1.8-5.3) 6.3 (1.3-30) 2.1 (1.2-3.8) -2.0 (1.1-4.0) -1.4 (P>0.05) --- *Odds ratios (for case-control design) or relative risk (for registry design) and 95% confidence intervals Subtype abbreviations: NHL (non-Hodgkin lymphoma); CLL (chronic lymphocytic leukemia/small lymphocytic lymphoma); DLBCL (diffuse large B-cell lymphoma); FL (follicular lymphoma); LPL/WM (lymphoplasmacytic lymphoma/Waldenstrom Macroglobulinemia); MZL (marginal zone lymphoma); MCL (mantle cell lymphoma); PTCL (peripheral T-cell lymphoma); HL (Hodgkin lymphoma). ‡ † Estimate not reported 28 From www.bloodjournal.org by guest on June 16, 2017. For personal use only. NHL From www.bloodjournal.org by guest on June 16, 2017. For personal use only. Table 2. GWAS-discovered loci for lymphoma Subtype CLL CLL CLL CLL CLL CLL CLL CLL CLL CLL CLL CLL CLL CLL CLL CLL CLL CLL CLL CLL CLL CLL CLL CLL CLL CLL CLL CLL CLL CLL CLL CLL FL FL FL FL FL FL FL FL FL FL FL DLBCL DLBCL DLBCL DLBCL DLBCL DLBCL MZL MZL HL HL HL (EBV-) HL HL HL (EBV+) HL (EBV+) HL HL HL (NS) HL (NS) Locus 2p22.2 2q13 2q13 2q33.1 2q37.1 2q37.3 3q26.2 4q25 4q26 5p15.33 6p21.31 6p21.32 6p21.32 6p25.3 6q25.2 7q31.33 8q22.3 8q24.21 9p21.3 10q23.31 11p15.5 11q24.1 12q24.13 15q15.1 15q21.3 15q23 16q24.1 16q24.1 18q21.32 18q21.33 18q21.33 19q13.32 3q28 6p21.32 6p21.32 6p21.32 6p21.32 6p21.33 6p21.33 8q24.21 11q23.3 11q24.3 18q21.33 2p23.3 3q27 6p21.33 6p25.3 8q24.21 8q24.21 6p21.32 6p21.33 2p16.1 3p24.1 5q31 6p21 6p21 6p21 6p21 6p21.32 6p21.32 6p21.32 6p21.32 SNP rs3770745 rs13401811 rs17483466 rs3769825 rs13397985 rs757978 rs10936599 rs898518 rs6858698 rs10069690 rs210142 rs9273363 rs674313 rs872071 rs2236256 rs17246404 rs2511714 rs2456449 rs1679013 rs4406737 rs7944004 rs735665 rs10735079 rs8024033 rs7169431 rs7176508 rs305061 rs2292982 rs4368253 rs4987855 rs4987852 rs11083846 rs6444305 rs10484561 rs2647012 rs17203612 rs3130437 rs6457327 rs13254990 rs4938573 rs4937362 rs17749561 rs79480871 rs6773854 rs2523607 rs116446171 rs13255292 rs4733601 rs9461741 rs2922994 rs1432295 rs3806624 rs20541 rs2248462 rs2395185 rs2734986 rs6904029 rs2281389 rs6903608 rs2858870 rs204999 Nearest Gene QPCT, PRKD3 ACOXL, BCL2L11 ACOXL, BCL2L11 CASP10/CASP8 SP140, SP110 FARP2 MYNN LEF1 CAMK2D TERT BAK1 HLA-DQB1 HLA-DRB5 IRF4 IPCEF1 POT1 ODF1 CASC19 CDKN2B-AS1 ACTA2, FAS C11orf21 GRAMD1B OAS3 BMF RFX7 RPLP1 IRF8 IRF8 PMAIP1 BCL2 BCL2 PRKD2 LPP MHC class II HLA-DQB1 HLA-DRβ1 Glu-28 HLA-DRA HLA-C C6orf15 et al. (STG) PVT1 CXCR5 ETS1 BCL2 NCOA1 BCL6/LPP HLA-B EXOC2 PVT1 PVT1 BTNL2 HLA-B REL EOMES IL13 MICB HLA-DRA HLA-A HCG9 HLA-DPB1 HLA-DRA HLA-DRB1 PRRT1 RAF† (controls) 0.22 0.81 0.20 0.45 0.19 0.11 0.75 0.59 0.16 0.25 0.70 0.27 0.26 0.54 0.44 0.71 0.41 0.36 0.52 0.57 0.49 0.21 0.36 0.51 0.08 0.37 0.66 0.34 0.69 0.91 0.06 0.22 0.27 0.13 0.44 0.30 0.49 0.62 0.38 0.32 0.20 0.46 0.91 0.076 0.22 0.12 0.019 0.32 0.48 0.018 0.11 0.40 0.45 0.18 0.22 0.33 0.18 0.30 0.83 0.27 0.13 0.27 29 ‡ OR 1.24 1.41 1.39 1.19 1.41 1.39 1.26 1.20 1.31 1.20 1.40 1.24 1.69 1.54 1.23 1.22 1.16 1.26 1.19 1.27 1.20 1.45 1.18 1.22 1.36 1.37 1.22 0.65 1.19 1.47 1.41 1.35 1.21 1.95 0.64 1.86 1.44 1.23 0.59 1.18 1.34 1.19 1.34 1.34 1.47 1.32 2.20 1.22 1.18 2.66 1.64 1.22 1.26 1.53 0.61 0.56 2.45 0.46 1.73 1.70 0.40 0.60 ‡ P-value −8 1.68 x 10 −18 2.08 x 10 –10 2.36 x 10 −9 2.50 x 10 –10 5.40 x 10 −9 2.11 x 10 -9 1.74 x 10 −10 4.24 x 10 -9 3.07 x 10 -10 1.12 x 10 -16 9.47 x 10 -10 2.24 x 10 -9 6.92 x 10 –20 1.91 x 10 -10 1.50 x 10 -8 3.40 x 10 -9 2.90 x 10 −10 7.84 x 10 −8 1.27 x 10 −14 1.22 x 10 2.15 x 10−10 3.78 x 10–12 2.34 x 10−8 2.71 x 10−10 4.74 x 10−7¶ 4.54 x 10–12 3.60 x 10−7¶ 6.48 x 10-9 2.51 x 10−8 2.66 x 10−12 7.76 x 10−11 3.96 x 10–9 1.10 x 10-10 1.12 x 10-29 2.00 x 10-21 7.89 x 10-69 4.59 x 10-16 8.23 x 10-9 4.70 x 10-11 1.06 x 10-8 5.79 x 10-20 6.76 x 10-11 8.28 x 10-10 4.23 x 10-8 1.14 x 10-11 2.40 x 10-10 2.33 x 10-21 9.98 x 10-13 3.63 x 10-11 3.95 x 10-15 2.43 x 10-9 1.91 x 10−8 1.14 x 10-12 5.40 × 10–9 1.30 x 10-13 8.30 x 10-25 1.20 x 10-15 5.50 x 10-10 6.31 x 10-13 2.84 × 10−50 5.61 x 10-9 2.34 x 10-8 Reference 55 Berndt et al. (2013) 55 Berndt et al. (2013) 57 Di Bernardo et al. (2008) 55 Berndt et al. (2013) 57 Di Bernardo et al. (2008) 58 Crowther-Swanepoel et al. (2010) 61 Speedy et al. (2014) 55 Berndt et al. (2013) 61 Speedy et al. (2014) 61 Speedy et al. (2014) 60 Slager et al. (2012) 55 Berndt et al. (2013) 59 Slager et al. (2011) 57 Di Bernardo et al. (2008) 61 Speedy et al. (2014) 61 Speedy et al. (2014) 61 Speedy et al. (2014) 58 Crowther-Swanepoel (2010) 55 Berndt et al. (2013) 55 Berndt et al. (2013) Berndt et al. (2013)55 Di Bernardo et al. (2008)57 Sava et al. (2014)62 Berndt et al. (2013)55 Crowther-Swanepoel et al. (2010)58 Di Bernardo et al. (2008)57 Crowther-Swanepoel et al. (2010)58 Slager et al. (2011)59 Berndt et al. (2013)55 Berndt et al. (2013)55 Berndt et al. (2013)55 Di Bernardo et al. (2008)57 Skibola et al. (2014)67 Conde et al. (2010)65 Smedby et al. (2011)66 Skibola et al. (2014)67 Skibola et al. (2014)67 Skibola et al. (2014)67 Skibola et al. (2009)64 Skibola et al. (2014)67 Skibola et al. (2014)67 Skibola et al. (2014)67 Skibola et al. (2014)67 Cerhan et al. (2014)82 Tan et al. (2013)80 Cerhan et al. (2014)82 Cerhan et al. (2014)82 Cerhan et al. (2014)82 Cerhan et al. (2014)82 Vijai et al. (2015)83 Vijai et al. (2015)83 Enciso-Mora et al. (2010)70 Frampton et al. (2013)73 Urayama et al. (2012)69 Urayama et al. (2012)69 Urayama et al. (2012)69 Urayama et al. (2012)69 Urayama et al. 2012)69 Moutsianas et al. (2011)76 Enciso-Mora et al. (2010)70 Cozen et al. (2012)71 Cozen et al. (2012)71 From www.bloodjournal.org by guest on June 16, 2017. For personal use only. HL 6q23.3 HL 8q24.21 HL 10p14 HL 19p13.3 LYM 11q12.1 *Subtype abbreviations: rs7745098 rs2019960 rs501764 rs1860661 rs12289961 HBS1L, MYB PVT1 GATA3 TCF3 LPXN 0.48 0.23 0.19 0.41 0.28 1.21 1.33 1.25 0.81 1.29 -9 3.42 x 10 1.26 x 10−13 −8 7.05 x 10 -10 3.50 x 10 3.89 x 10-8 73 Frampton et al. (2013) Enciso-Mora et al. (2010)70 70 Enciso-Mora et al. (2010) 72 Cozen et al. (2014) Vijai et al. (2013)84 CLL (chronic lymphocytic leukemia/small lymphocytic lymphoma); FL (follicular lymphoma); DLBCL (diffuse large B-cell lymphoma); MZL (marginal zone lymphoma); HL (Hodgkin lymphoma), NS (nodular sclerosis); LYM (lymphoma). † Risk allele frequency among controls Odds Ratio (per allele) Considered genome-wide significant at the time of initial publication ‡ ¶ 30 From www.bloodjournal.org by guest on June 16, 2017. For personal use only. Figure 1. GWAS-discovered loci for lymphoma subtypes mapped to chromosomal location. Except for 6p21 and 8q24, there is minimal little overlap of loci for lymphoma subtype-specific susceptibility loci. 31 From www.bloodjournal.org by guest on June 16, 2017. For personal use only. nds Figure 2. Lymphoma susceptibility loci by effect size and allele frequency. The blue diamond represent established lymphoma susceptibility loci plotted by allele frequency (x-axis) versus effect ct size (y-axis). For lymphoma, most of the loci are common variants of low to modest effect size ave (mainly discovered by genome-wide association studies), although a few low-frequency variants hav been identified. No rare alleles of low frequency (generally identified through linkage studies and sequencing) have been definitively linked to lymphoma. Very rare variants of low effect size are difficult to identify using current genetic approaches, while there are very few examples of common n variants of high effect size for common diseases (and none in lymphoma). 32 From www.bloodjournal.org by guest on June 16, 2017. For personal use only. Prepublished online September 24, 2015; doi:10.1182/blood-2015-04-537498 Familial predisposition and genetic risk factors for lymphoma James R. Cerhan and Susan L. 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