Etiology and pathogenesis of neoplasia,
premalignant lesions, physical, chemical
& microbial carcinogens
Dr Sowmya Uthaiah
Assistant professor
Dept of Pathology
Epidemiology of cancer
 12.7 million new cancer cases worldwide, leading to 7.6 million
deaths (21,000 deaths per day)
 Geographic variation in the incidence of specific cancers-
differences in exposure to environmental carcinogens
 Men - prostate, lung, and colon/rectum.
 Women - cancers of the breast, lung, and colon/rectum
Race –
 Disparity in cancer mortality rates between white and black
americans
 African americans – largest decline in cancer mortality
during the past decade
 Hispanics living in the united states - lower frequency of the
most common tumors seen in the white non-hispanic
population but a higher incidence of tumors of the stomach,
liver, uterine cervix, gallbladder & leukemias.
Environmental Factors
 Both genetic and environmental factors
 Environmental influences appear to be the dominant risk factors
 Wide geographic variation in the incidence of specific forms
of cancer
 most common tumor of men in the United States and developed
world - prostate cancer
 developing world- cancers of the liver, stomach, esophagus,
bladder, lung, oropharynx, and the immune system
 breast cancer - higher in women in developed countries than in
developing world
Environmental factors affecting cancer risk are the
following:
1. Infectious agents
 15% of all - directly or indirectly by
infectious agents
 three times higher in the developing
world than in the developed world
 Human papilloma virus (HPV)-
sexual contact- cervical carcinoma
and head and neck cancers
2. Smoking
 Cigarette smoking- most important environmental factor
contributing to premature death in the United States
 Lung cancer deaths (90%)
 Cancer of the mouth
 Pharynx
 Larynx
 Esophagus
 Pancreas
 Bladder
3. Diet
 wide geographic variation in the incidences
of
colorectal
carcinoma, prostate
carcinoma, and breast carcinoma
4. Obesity
 weight is strongly associated with cancer
risk
 obese U.S. population have 52% (men) to
62% (women) higher death rates from
cancer
 approx 14% of cancer deaths in men and
20% in women can be attributed to
obesity.
5. Reproductive history
 Lifelong
cumulative exposure to estrogen stimulation,
particularly if unopposed by progesterone
 risk of cancers of the breast and endometrium - tissues
responsive to these hormones
 timing and number of pregnancies a woman has during her
lifetime - differences in breast cancer incidence
6. Environmental carcinogens
 Ultraviolet [UV] rays, smog
 Drinking well water (eg: Arsenic, particularly in Bangladesh)
 Medications (eg: Methotrexate)
 Work - asbestos
 Grilled meat, high-fat diet, alcohol
“IT APPEARS THAT ALMOST EVERYTHING ONE DOES TO
EARN A LIVELIHOOD OR FOR PLEASURE IS FATTENING,
IMMORAL, ILLEGAL, OR, EVEN WORSE, CARCINOGENIC!”
Age
 Most carcinomas occur in the later years of life (>55 years)
 Cancer related death : women aged 40 to 79 and men aged 60 to 79
 Accumulation of somatic mutations over the years
 Decline in immune competence with ageing
 Cancer accounts for slightly more than 10% of all deaths in children
younger than age 15 in the united states - acute leukemia and
distinctive neoplasms of the central nervous system
 Common neoplasms of infancy and childhood - so-called small round
blue cell tumors such as neuroblastoma, wilms tumor,
retinoblastoma, acute leukemias, and rhabdomyosarcomas.
Acquired Predisposing Conditions
1. Chronic inflammation
2. Precursor lesions
3. Immunodeficiency states
Chronic inflammation and cancer
 First proposed by virchow in 1863
 Tissue injury----- compensatory proliferation of cells -----repair the
damage----- increase the pool of tissue stem cells ----- susceptible to
transformation.
 Activated immune cells-----reactive oxygen & inflammatory
mediators----- directly genotoxic----- genomic damage
 Chronic epithelial injury----- metaplasia
Eg: Helicobacter pylori gastritis – gastric cancer
Precursor lesions and cancer
 Precursor lesions can be defined as localized morphologic changes
that are associated with a high risk of cancer
 Barrett esophagus - gastric and colonic metaplasia of the esophageal
mucosa in gastric reflux
 Squamous metaplasia
 Bronchial mucosa - smoking
 Bladder mucosa - schistosomiasis infection
 Colonic metaplasia of the stomach – pernicious anemia and chronic
atrophic gastritis
 Leukoplakia - thickening of squamous epithelium in oral cavity,
penis or vulva ---squamous cell carcinoma.
 Endometrial hyperplasia----non inflammatory hyperplasias-
sustained estrogenic stimulation of the endometrium--endometrial carcinoma
 Colonic villous adenoma – colon carcinoma
Immunodeficiency states and cancer
 T-cell immunity deficient individuals- cancers- oncogenic viruses. –
- lymphomas
- carcinomas
- sarcomas
- sarcoma-like proliferations
Physical, chemical and
microbiological carcinogenesis
Dr Sowmya B U
Assistant professor
Dept of Pathology
Physical carcinogens- Radiation Carcinogenesis
1.UV rays of sunlight



3.Particulate radiation
2.Ionizing electromagnetic
Ultraviolet Rays
 Derived from the sun
 Fair-skinned individuals
 Squamous cell carcinoma
 Basal cell carcinoma
 Melanoma of the skin
Factors affecting
 type of UV rays
 the intensity of exposure
 quantity of the light-absorbing “protective mantle” of melanin in the
skin
 Non-melanoma skin cancers - total cumulative exposure to UV
radiation
 Melanomas - intense intermittent exposure – eg: sunbathing
UV RAYS
WAVELENGTH
UVA
320-400 nm
UVB
280-320 nm
UVC
200-280 nm
 UVB - induction of cutaneous cancers
 UVC - potent mutagen but filtered out by the ozone layer
Carcinogenicity of UVB light
 Formation of pyrimidine dimers in DNA
energy in a photon of UV light is absorbed by DNA
Chemical reaction leads to covalent crosslinking of pyrimidine
bases, particularly adjacent thymidine residues in the same
strand of DNA
distorts the DNA helix
prevents proper pairing of the dimer with bases in the opposite
DNA strand
 Pyrimidine dimers are repaired by the nucleotide excision repair
pathway
 Excessive sun exposure ---- capacity of the nucleotide excision
repair pathway is overwhelmed --- error-prone nontemplated
DNA-repair mechanisms----survival of the cell at the cost of
genomic mutations ----- lead to cancer
Ionizing Radiation
 Electromagnetic (x-rays, γ rays) and particulate (α particles, β
particles, protons, neutrons)
 X-rays - skin cancers
 Miners of radioactive elements in central Europe and the Rocky
Mountain region of United States- 10 fold increase lung cancers
 Hiroshima and Nagasaki- leukemias, carcinomas of the breast,
colon, thyroid, and lung
 Computerized tomography (CT scans)- children
 2-3 scans - 3 fold higher risk of leukemia
 5-10 scans - 10 fold higher risk of brain tumors
Ionizing radiation induced
cancers
 Myeloid leukemias – MC
 Cancer of the thyroid (young)
 Cancers of the breast, lungs, and
salivary glands
 Skin, bone, gastrointestinal tract –
rare
“practically
any cell can be
transformed into a cancer cell by
sufficient exposure to radiant
energy”
Chemical carcinogenesis
Carcinogens
Synthetic
Naturally occurring
Directly acting (no metabolic
activity)
Indirectly acting (procarcinogens,
needs metabolic activity)
Initiators (irreversible DNA
damage)
Promoters (reversible non DNA
damage)
Major Chemical Carcinogens
 Direct-Acting Carcinogens
 Alkylating Agents
 Anticancer drugs (cyclophosphamide , chlorambucil , nitrosoureas)
 β-Propiolactone, Dimethyl sulfate, Diepoxybutane
 Acylating Agents
 1-Acetyl-imidazole, Dimethylcarbamyl chloride
 Procarcinogens That Require Metabolic Activation
 Polycyclic and Heterocyclic Aromatic Hydrocarbons
 Benz(a)anthracene, Benzo(a)pyrene, Dibenz(a,h)anthracene,
 3-Methylcholanthrene, 7,12-Dimethylbenz(a)anthracene
 Aromatic Amines, Amides, Azo Dyes
 2-Naphthylamine (β-naphthylamine), Benzidine, 2-Acetylaminofluorene,
Dimethylaminoazobenzene (butter yellow)
 Natural Plant and Microbial Products
 Aflatoxin B, Griseofulvin, Cycasin, Safrole, Betel nuts
 Others
 Nitrosamine and amides, Vinyl chloride, nickel, chromium, Insecticides, fungicides,
Polychlorinated biphenyls
Carcinogenic chemicals
Direct acting alkylating agents
 Activation dependent, weak carcinogens
 Used as anticancer drugs
 Induce lymphoid neoplasms, leukemia etc.,
 Powerful immunosuppressive agents
 Ex: Cyclophosphamide Busulfan
 Interact with DNA and damage
Carcinogenic chemicals
Polycyclic aromatic hydrocarbons
 Source: combustion of smoke, smoked meat, animal fat





processing , broiled meat, smoked fish
Induce lung and bladder cancer
Most potent carcinogens known
Require metabolic activation
Skin paint- skin cancer
Subcutaneous injection-sarcoma
Carcinogenic chemicals
Aromatic amines & azo dyes
 Source: food coloring agents
Eg: Butter yellow, Scarlet red
 Beta naphthylamine – rubber industry- bladder cancer.
Carcinogenic chemicals
Naturally occurring carcinogens
 Source; moldy grains, peanuts, rice-aspergillus flavus- aflatoxin B1.
 Potent hepatocarcinogen
 Correlates with increased incidence in china/ Africa.
Carcinogenic chemicals
Nitrosamines and amides
 Source:
Nitrostable amines and nitrates used as food preservative- bacteria
convert them to nitrites
 Induce gastric cancers
Carcinogenic chemicals miscellaneous
agents
Asbestos - Bronchogenic ca , ca.mesothelioma, GI cancers
Asbestos + smoking - many fold risk ca lung
Vinyl chloride- hemangiosarcoma liver
Chromium & nickle- Ca lung - volatile industrial environment pollutant
Arsenic – skin cancer
Hormones – endometrial cancer.
Initiation
 Induction of mutation in genome of cells
 Initiated cells are not transformed cells
 They have no growth autonomy/unique phenotypic #.
 In contrast to normal cells, can give rise to tumors when
appropriately stimulated by promoting agents
Promotion of carcinogenesis
 Process of tumor induction in a previously initiated cell by
chemicals.
 The effect of promoters is short lived and reversible.
 They do not affect DNA.
 Non tumorigenic by themselves.
Eg: Phenols, artificial sweeteners
 No sudden change
 Need sufficient time and dose
 Changes reversible
 Enhance the effect of carcinogens
 Acts through growth factor pathway
Promotion of carcinogenesis
 Tumor promotion steps- multiple steps
Proliferation of preneoplastic cells
 Malignant conversion
 Tumor progression (depends on cells & stroma)

 Involved in clonal expansion and aberrant differentiation of




initiated cells
The effect of promoters are pleiotropic
Induction of cell proliferation is a sine qua none phenomenon of
promoters
They act via signal transduction pathways eg. protein kinase C
Activation of PKC - series of phosphorylations- cell proliferation
and differentiation
Chemical Carcinogen - Mechanism
 Reactive electrophiles
 Electron deficient substances
 Binds with electron rich portions of cells (DNA)
 Target molecules
 DNA – mutation - carcinogenesis
 Initiated cell
Unrepaired DNA damage
One cycle of proliferation
Irreversible damage
Vulnerable to promotion
Concept of initiation and promotion
sequence
 Initiation - exposure of cells to sufficient dose of carcinogen
 Potential to induce tumor
 Initiation alone is insufficient
 Permanent DNA damage- mutation.
 Rapid and irreversible
 Promoters can induce tumor in an initiated cell, by themselves are
not tumorigenic
 The cellular changes resulting from application of promoters do
not affect DNA directly and are reversible.
Property of direct acting & ultimate
carcinogens
 Require no metabolic conversion
 Highly reactive electrophiles (electron deficient) react with
nucleophilic ( electron rich) sites in the cell.
 Non enzymatic reactions- covalent adducts b/n carcinogen &
nucleotide DNA.
 Electron rich sites in cell; DNA, RNA,proteins
Indirect – acting carcinogens- Metabolic action of
carcinogens
 Most carcinogens need activation to form ultimate carcinogens
 Other metabolic pathways detoxify (eg: cytochrome P-450-
dependent mono-oxygenases)
 Carcinogenic potency
a) inherent reactivity of electrophilic derivative
b) balance b/n metabolic activation and inactivation.
 Carcinogenesis is regulated in part by polymorphism in the genes
that encode the genes
 Age, sex and nutritional status determine the internal dose of
toxicants
Molecular targets of chemical carcinogens
 Mutations affecting oncogenes,tumor suppressor genes and
genes that regulate apoptosis and genes involved in DNA
repair
 DNA is the primary target
 No single or unique alteration @ with initiation
 Each class of carcinogen produces limited pattern of DNA
damage
 Each carcinogen produces molecular ‘fingerprint’ that links
specific chemical with their mutational effect.
Initiated cell
 Unrepaired DNA alterations are essential first step in
initiating tumor
 Damaged DNA template must replicate to be inheritable and
permanent
 Quiescent cells may never be affected by carcinogens, unless
mitogenically stimulated
 Concurrent exposure to viruses, parasites, hormones induce
proliferation
Tests for Chemical Carcinogenecity
 Experimental induction
 Animals: Initiator……Promoter
 Tests for mutagenicity (Ames Test)
 In vitro test
 Ability of potential carcinogens to induce mutations in selected
strains of salmonella typhimurium
Microbiological carcinogenesis
Microbiological Carcinogens
 Oncogenic Viruses
 DNA





Human Papilloma Virus
EB virus
HHV 8
Hepatitis B
Pox virus
Papilloma, Ca. of cervix, skin
Lymphoma, Nasopharyngeal carcinoma
Kaposi sarcoma, B cell lymphoma
Hepatocellular carcinoma
Molluscum contagiosum, Papilloma
 RNA
 HTLV 1
 HTLV 2
 Hepatitis C
Adult T cell Leukemia/Lymphoma
T cell variant of Hairy cell leukemia
Hepatocellular carcinoma
 Oncogenic Bacteria
 H. pylori
Gastric lymphoma, Adenocarcinoma
Human T-cell leukemia virus type -1
 adult T-cell leukemia/lymphoma (ATLL)
 Endemic - Japan, the Caribbean basin, South America, and Africa
 Sporadic- United States
 transmission of infected T cells via sexual intercourse, blood
products, or breastfeeding
 Leukemia develops in only 3% to 5% of the infected individuals
 long latent period of 40 to 60 years
Pathogenesis
 viral integration shows a clonal pattern
 HTLV-1 genome contains the gag, pol, env, tax and longterminal-
repeat regions typical
 Tax gene is essential for viral replication
 stimulates transcription of viral RNA from the 5′ long terminal
repeat
 alters the transcription of several host cell genes and interacts with
certain host cell signaling proteins
1. Increased pro-growth signaling and cell survival
 Tax interacts with PI3K - stimulates AKT - kinases participate in
the cascade - promotes cell survival and cell growth
 Upregulates the expression of cyclin D2
 represses the expression of multiple CDK inhibitors
 Activates the transcription factor NF-κB - promotes the survival
of many cell types, including lymphocytes
2. Increased genomic instability
 interfering with DNA-repair functions
 inhibiting cell cycle checkpoints activated by DNA damage
stimulatory
effects of
Tax on cell
proliferatio
n
expansion
of a
nonmaligna
nt
polyclonal
cell
population
proliferatin
g T cells are
at increased
risk of
mutations
genomic
instability
accumulati
on
of
mutations
and
chromoso
mal
abnormaliti
es
monoclonal
neoplastic
T-cell
population
emerges.
Human papilloma virus
 Type 1,2,4 & 7 - squamous papilloma
 Type 16,18,& less commonly 31,33,35,51 - 85% of
squamous cell carcinoma and their precursors
 Type 6 & 11 - genital wart of low malignant potential
Pathogenesis
 high-risk HPV types express oncogenic proteins that inactivate
tumor suppressors, activate cyclins, inhibit apoptosis, and combat
cellular senescence
 Viral oncoproteins E6 & E7
Oncogenic activities of E6
 The E6 protein binds to and mediates the degradation of p53
 Stimulates the expression of TERT, the catalytic subunit of
telomerase
 E6 from high-risk HPV types has a higher affinity for p53 than E6
from low-risk HPV types
 Human TP53 is polymorphic at codon 72, encoding either a
proline or arginine residue
 The p53 Arg72 variant is much more susceptible to degradation by
E6 - more likely to develop cervical carcinomas
Oncogenic activities of E7
 speeding cells through the G1-S cell cycle checkpoint
 binds to the RB protein and displaces the E2F transcription
factors (normally sequestered by RB) – progression of cell cycle
 E7 also inactivates the CDK inhibitors p21 and p27
 E7 proteins from highrisk HPVs (types 16, 18, and 31) - bind and
activate cyclins E and A
 E7 proteins from high-risk HPV types have a higher affinity for RB
than do E7 proteins from low-risk HPV types
Epstein-Barr Virus
 Member of herpes virus family
Causes :
 African Burkitt’s Lymphoma
 B- cell lymphoma in immunosuppressive patient
 Some cases of Hodgkin's Lymphoma
 Nasopharyngeal carcinomas
Primary infection
 Here EBV infect epithelial cells of oropharynx
 Later virus reaches sub-epithelium and infect B-Cells
CD-21 molecule.
 There virus multiply and causes cell lysis and infect
more B-cells in the circulation.
EBV infection
Acute infection
Latent infection
Latent infection
Several features are important for
maintenance of latency and oncogenicity

Virus must be able to maintain their viral
genome in the cell

Virus must avoid killing the cell

Virus must avoid destruction of cell by host
immune mechanism

Virus must activate host cellular growth
regulatory pathway.
This is achieved through
Maintaining multicopy circular episome or
integrated into host genome

EBV expresses limited no. of viral genes

By transactivating with cellular genes
Pathogenesis
1. Latent membrane protein-1 (LMP-1)
 behaves like a active CD40 receptor - recipient of helper T-cell
signals - stimulate B-cell growth
 activates the NF-κB and JAK/ STAT signaling pathways and
promotes B-cell survival and proliferation
 prevents apoptosis by activating BCL2
2. EBNA-2
 encodes a nuclear protein that mimics a constitutively active
Notch receptor
 transactivates cyclin D and the SRC family of proto-oncogenes
3. gene encoding a viral cytokine, vIL-10
 prevent macrophages and monocytes from activating T cells
EBV-dependent
 transformation of B cells
Mechanism of transformation
Latently infected B-cells
Express 6 nucleoproteins
EBNA-1, EBNA-2
EBNA-LP, EBNA-3A
EBNA-3B, EBNA-3C
EBNA-2
TRANSACTIVATES
SEVERAL HOST
GENES. e.g. cyclin-D
SRC family
2 membrane proteins
LMP-1
LMP-2
2 nontranslated RNA
EBER-1
EBER-2
LMP-1 (mimicking CD-40)
Promotes
transcription
of LMP-1
Activates signaling molecule
NFkB & JAK / STAT
Causes B-cell survival
& proliferation
Promotes resting
B cell from G0 to G1
B-cell IMMORTAL
Burkitt lymphoma
 > 90% of African tumor carry EBV
 Nonendemic areas 80% of tumors are unrelated to EBV
 100% patient have elevated antibody titer against viral
genome
 Serum antibody titer correlated with risk of developing tumor.
 EBV infection acts as a polyclonal B- cell mitogen, it sets the
stage for acquisition of 8:14 translocation and other mutation
which ultimately release the cells from normal growth regulation

Tumor progression involve
- P53 mutation
- defects affects the P14ARF/ MDM2/ P53
- inactivation of P16INK4a by deletion or
hyper methylation.

Immunosuppressive patients have more
chance of acquiring this tumor
Hepatitis virus
 hepatitis B and C virus infection - liver cancer
 70% to 85% of hepatocellular carcinomas worldwide
 HBV and HCV genomes do not encode any viral oncoproteins
 Oncogenic effects of HBV and HCV are multifactorial
 immunologically mediated chronic inflammation and
hepatocyte death leading to regeneration and, over time,
genomic damage
 unresolved chronic inflammation - the immune response may
maladaptive, promoting tumorigenesis
PATHOGENESIS
chronic viral infection
activated immune cells - growth factors,
cytokines, chemokines, and other
bioactive substances
promote cell survival, tissue remodeling,
and angiogenesis
compensatory proliferation of
hepatocytes
activation of the NF-Κb
pathway - blocks apoptosis,
allowing the dividing
hepatocytes to incur
genotoxic stress and to
accumulate mutations
activated immune cells
produce reactive oxygen
species -genotoxic and
mutagenic
HCC
HBV gene - HBx
activate a variety of
transcription factors and
several signal
transduction pathways
viral integration structural changes in
chromosomes dysregulate oncogenes
Hepatitis C Virus
 Less clearly understood
 Chronic liver cell injury
 Compensatory regeneration
 HCV core protein- direct effect on tumorigenesis - by activating a
variety of growth-promoting signal transduction pathways.
Helicobacter pylori
 gastric adenocarcinomas and gastric lymphomas
 increased epithelial cell proliferation in a background of chronic
inflammation
 chronic gastritis - gastric atrophy - intestinal metaplasia of the
lining cells – Dysplasia cancer
 sequence takes decades to complete and occurs in only 3% of
infected patients
 Strains associated with gastric adenocarcinoma - “pathogenicity
island” that contains cytotoxin-associated A (CagA) gene
 CagA penetrates into gastric epithelial cells - initiation of a
signaling cascade that mimics unregulated growth factor
stimulation
 Lymphomas of mucosa-associated lymphoid tissue, or MALTomas of B






cell origin
strain-specific H. pylori
host genetic factors, such as polymorphisms in the promoters of
inflammatory cytokines such as IL-1β and tumor necrosis factor (TNF)
H. pylori infection leads to the appearance of H. pylori-reactive T cells –
stimulate a polyclonal B-cell proliferation.
In chronic infections - unknown mutations - growth advantage - cells
grow out into a monoclonal “MALToma”
T-cell stimulation of B-cell pathways - activate the transcription factor
NF-κB.
At this stage, eradication of H. pylori by antibiotic therapy “cures” the
lymphoma by removing the antigenic stimulus for T cells
later stages - additional mutations acquired - constitutive NF-κB
activation
conclusion
 Carcinogenesis is a multistep process, which involve both
genetic susceptibility and interaction with environmental factors.
 Any one factor like chemical, radiational and microbiological
factors, usually doesn't induce transformation of normal cell to
neoplastic process.
 As we sail in a ocean of carcinogens, our body mechanisms are
usually nullify the threats but rarely induce cancer,