Osteosarcoma is a primary bone tumour composed of cells, which at least focally produce tumoral
bone (osteoid). It is, with the exception of plasmacytoma, the most frequent primary malignant bone
tumor having an incidence of 2.5 per million populations per annum. Children and young adults are
the most affected age group with a second incidence peak around the age of 60. More than 90 % of
osteosarcomas are of the conventional highly malignant type and the majority of them occur around
the knee followed by the humerus and pelvic bones. Approximately 7-10 % arise in the craniofascial
bones (maxilla and mandible). Osteosarcoma is rare in the spine and in the small bones of hands and
feet. The most common symptoms are bone mass, often with soft tissue involvement and pain.
The prognosis of osteosarcoma and the life quality of survivors has improved greatly in the last 20
years mostly due to the introduction of neo-adjuvant chemotherapy and to advances in limb-sparing
surgical techniques. A reliable and speedy diagnosis in cases of osteosarcoma is crucial in order to
quickly initiate adequate chemotherapy before surgical excision of the tumors.
Osteosarcomas show a wide variation in regard to their morphological appearance. Most common is
the conventional intramedullary subtype. Less common variants are periosteal osteosarcoma,
parosteal or juxctacortical osteosarcoma, central low-grade osteosarcoma, high grade surface
osteosarcoma and small cell osteosarcoma.
Cytologic features of high-grade osteosarcoma
Osteoblastic subtype
Variable cellularity
A mixture of single cells and clusters in moderately cellular smears
Moderately to highly pleomorphic rounded, ovoid, polygonal tumour cells
Osteoblast-like tumour cells with eccentric nuclei and a cytoplasmic ´Hof´
Clusters of epithelioid tumour cells with distinct cytoplasmic borders and rounded nuclei with
prominent nucleoli
Multinucleated tumour giant cells
Strands of osteoid matrix (red or purple in MGG, pale pink in HE) between
Mitoses, often atypical
Benign osteoclast-like giant cells; numerous in giant cell rich osteosarcoma
Occasional necrosis and calcifications
Chondroblastic subtype
Myxoid back ground matrix (red; red-violett in MGG)
An admixture of atypical mono-or binucleated chondroblast-like cells in addition to cells seen in
osteoblastic osteosarcoma
Occasionally fragments of hyaline cartilage with atypical cells in lacunae
Differential diagnosis
Reactive osteoblastic proliferations as in fracture callus
Pseudomalignant myositis ossificans
Osteoblastoma
Giant cell tumour (giant cell rich osteosarcoma, teleangiectatic osteosarcoma)
Aneurysmal bone cyst (telangiectatic osteosarcoma)
High grade malignant chondrosarcoma
Pleomorphic sarcoma (MFH-type, pleomorphic leiomyosarcoma)
Conventional Ewing´s sarcoma (small cell osteosarcoma)
Mesenchymal chondrosarcoma (small cell osteosarcoma)
Primary large cell anaplastic lymphoma in bone
Metastatic carcinoma
Metastatic melanoma
Comments
Reactive osteoblastic proliferations such as fracture callus and pseudomalignant myositis ossificans
are the most important benign lesions that can be mistaken for OS. Reactive osteoblasts in these
entities may be pleomorphic showing anisokaryosis and prominent nucleoli, but their chromatin
pattern is regular and the cytoplasmic ´Hof’ clearly visible. When the yield is poor and haemorrhagic
as may be the case in aspirates from telangiectatic osteosarcoma, osteoclast-like benign giant cells
may predominate and scattered obviously malignant cells may be overlooked and there is a risk that
the lesion could be misdiagnosed as an aneurysmal bone cyst. The multinucleated benign giant cells
present in giant cell rich osteosarcoma may be as numerous as in smears from giant cell tumours. It is
important to look for obvious malignant cells and atypical mitoses. Osteoblastoma-like osteosarcoma
is a diagnostic challenge in biopsy samples and even more so in FNA material. When the radiologic
features in these cases are not unequivocally malignant, the cytological diagnosis is better reported
as inconclusive than suspicious for osteosarcoma. The tumour cells of conventional osteosarcoma
may exhibit epithelioid features such as distinct cell borders and rounded or ovoid nuclei with
prominent nucleoli and when they are clustered they can mimic cells from metastatic carcinoma.
Especially metastatic renal carcinoma can produce an extracellular matrix which can be easily
confused with osteoid. Anaplastic large cell lymphoma can arise primarily in bone and may feature
large cytoplasm-rich, rounded cells with eccentric nuclei and prominent nucleoli resembling highly
atypical osteoblast-like tumour cells. Antibodies to keratin, S-100-protein, HMB45, Melanin A, EMA,
ALK, CD45 and CD30 are suitable markers in the differential diagnosis of carcinoma, malignant
melanoma and ALCL, respectively.
The clue to the cytological diagnosis of conventional osteosarcoma in routinely stained smears is the
presence of intercellular osteoid and osteoblast-like tumour cells. Osteoid is best appreciated in
MGG-stained smears. To confirm diagnosis it is at times necessary to supplement the routine stains
with ancillary techniques. Strong intracytoplasmatic alkaline phosphatase staining (ALP) in tumour
cells confirms their osteoblastic differentiation. ALP-staining is of great help in the differential
diagnosis between chondroblastic osteosarcoma and high grade malignant (Grade III)
chondrosarcoma as well as in the distinction from metastatic carcinoma or melanoma and from
anaplastic large cell lymphoma. Differentiating osteoid from collagenous matrix can occasionally be
difficult. Electron microscopic examination, is another well-established method to define osteoid in
fine needle aspirates.
Cell blocks preserved the architecture of the tumor tissue including calcification and osteoid. Cell
block can help in the clarification of diagnosis, especially when one can see both malignant cells and
strands of osteoid in the cellblock section.
Conclusions
FNAC is an efficient method in the diagnosis of high-grade osteosarcoma. The final conclusion must
be based on the combined evaluation of clinical and radiographic data and the cytologic examination,
often supplemented with ancillary techniques.
Primary investigation and treatment including cytologic or histopathologic diagnosis of
osteosarcoma, should be preferably performed at multidisciplinary centers. The optimal use of fine
needle aspiration as a pre-treatment diagnostic tool requires the referral of patients to such centers
where the cytopathologist is a member of the team, and where there is close cooperation between
cytopathologist, radiologist, surgeon and oncologist.
References
1. Soderlund V, Skoog L, Unni KK, Bertoni F, Brosjo O, Kreicbergs A: Diagnosis of high-grade
osteosarcoma by radiology and cytology: a retrospective study of 52 cases. Sarcoma 2004, 8(1):3136.
2. Klijanienko J, Caillaud JM, Orbach D, Brisse H, Lagace R, Sastre-Gareau X: Cyto-histological
correlations in primary, recurrent, and metastatic bone and soft tissue osteosarcoma. Institut Curie's
experience. Diagn Cytopathol 2007, 35(5):270-275.
3. Britt T, Clifford C, Barger A, Moroff S, Drobatz K, Thacher C, Davis G: Diagnosing appendicular
osteosarcoma with ultrasound-guided fine-needle aspiration: 36 cases. J Small Anim Pract 2007,
48(3):145-150.
4. Barger A, Graca R, Bailey K, Messick J, de Lorimier LP, Fan T, Hoffmann W: Use of alkaline
phosphatase staining to differentiate canine osteosarcoma from other vimentin-positive tumors. Vet
Pathol 2005, 42(2):161-165.
5. Domanski HA, Akerman M: Fine-needle aspiration of primary osteosarcoma: a cytologicalhistological study. Diagn Cytopathol 2005, 32(5):269-275.
6. Dodd LG, Scully SP, Cothran RL, Harrelson JM: Utility of fine-needle aspiration in the diagnosis of
primary osteosarcoma. Diagn Cytopathol 2002, 27(6):350-353.
7. Kilpatrick SE, Ward WG, Bos GD, Chauvenet AR, Gold SH: The role of fine needle aspiration biopsy
in the diagnosis and management of osteosarcoma. Pediatr Pathol Mol Med 2001, 20(3):175-187.
8. Koh JS, Chung JH, Kweon MS, Lee SS, Lee SY, Lee JH: Fine needle aspiration cytology of late -stage
callus in stress fracture. A case report. Acta Cytol 2001, 45(3):445-448.
9. Agarwal S, Agarwal T, Agarwal R, Agarwal PK, Jain UK: Fine needle aspiration of bone tumors.
Cancer Detect Prev 2000, 24(6):602-609.
10. Nicol KK, Ward WG, Savage PD, Kilpatrick SE: Fine-needle aspiration biopsy of skeletal versus
extraskeletal osteosarcoma. Cancer 1998, 84(3):176-185.
11. Willen H: Fine needle aspiration in the diagnosis of bone tumors. Acta Orthop Scand Suppl 1997,
273:47-53.