Background/aims
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.
Participants and methods
Periodic acid-Schiff (PAS), CD99, CD138, osteocalcin, and leukocyte common
antigen (LCA) were evaluated in 113 patients with RCTB.
Results
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%).
Conclusion
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.