RESUMO
Background/Aims: Differential diagnosis between aggressive osteoblastoma and low grade osteosarcoma may be very diffi cult or even impossible on a small biopsy. This study was designed to assess the usefulness of immunoexpression of COX-2 and osteocalcin in the differential diagnosis of the two tumour types. Methods: Immunostaining of COX 2 and osteocalcin were studied in 9 osteoblastomas and 30 osteosarcomas. Results: All osteoblastomas and 11/20 (55%) high-grade osteosarcomas showed COX-2 immunoreactivity. All low grade osteosarcomas were COX-2 negative. COX-2 was signifi cantly higher (p<0.002) in osteoblastomas 9/9 (100%) than in osteosarcomas 13/30 (43%) and in aggressive osteoblastomas versus low grade osteosarcomas (p<0.01). Osteocalcin was found in tumour cells of all osteosarcomas and osteoblastomas and in the osteoid matrix of 84% of osteosarcomas and 78% of osteoblastomas. Strong osteocalcin was signifi cantly higher (p<0.02) in osteoblastomas (78%) than in osteosarcomas (27%). Conclusion: COX-2 is a valuable marker in distinction between osteosarcoma and osteoblastoma. Negative COX-2 could confi rm the diagnosis of low grade osteosarcoma versus aggressive osteoblastoma. Intensity and distribution of osteocalcin may indicate the degree of osteoblastic differentiation.
RESUMO
The differential diagnosis of round cell tumors of bone [RCTB], Ewing sarcoma, smallcell osteosarcoma, mesenchymal chondrosarcoma, osteoblastoma, chondroblastoma, primary bone lymphoma, and multiple myeloma still remains a challenge. Given the significant differences in treatment, an accurate diagnosis is crucial. This study aimed to evaluate some histochemical and immunohistochemical criteria of RCTB. Periodic acid-Schiff [PAS], CD99, CD138, osteocalcin, and leukocyte common antigen [LCA] were evaluated in 113 patients with RCTB. PAS was positive in neoplastic cells of all Ewing sarcomas, 27% of osteosarcomas, 92% of chondrosarcomas, all osteoblastomas and chondroblastomas, and the osteoid tissue of all osteosarcomas and osteoblastomas. CD99 was positive in all Ewing sarcomas, in 11, 4, and 11% of osteoblastomas, multiple myelomas, and bone lymphomas, respectively. CD99 was higher in Ewing sarcoma than in other RCTB [Po0.0001]. Osteocalcin was positive in neoplastic cells of all osteosarcomas, osteoblastomas, and 20% of chondroblastomas, 84, and 78% of osteoid of osteosarcomas and osteoblastomas, respectively. CD138 was positive in all multiple myelomas, 12% of Ewing sarcomas, 20% of osteosarcomas, 44% of osteoblastomas, 8% of chondrosarcomas, and 40% of chondroblastomas. CD138 was higher in multiple myeloma [Po0.0001] than in other RCTB. LCA positivity was higher [Po0.01] in bone lymphomas [100%] than in multiple myelomas [73%]. PAS negativity excludes multiple myeloma and bone lymphoma from other RCTB that could be differentiated by LCA and CD138. CD99 positivity confirms the diagnosis of Ewing sarcoma. PAS could detect areas of osteoid in osteosarcoma and osteoblastoma. Osteocalcin suggests an osteogenic tumor origin: osteosarcoma/ osteoblastoma. Double negativity of CD99 and osteocalcin suggests a chondrogenic tumor origin: chondrosarcoma/chondroblastoma