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