Seventy-nine cases of small round cell
tumors involving bone were studied in an attempt to learn whether the immunohistochemical features of the lesions might allow distinction of small cell
osteosarcoma from other potential differential diagnostic considerations, including
Ewing's sarcoma, atypical
Ewing's sarcoma,
primitive neuroectodermal tumor,
mesenchymal chondrosarcoma,
lymphoma, and the
Askin tumor. The tissues studied were all
formalin-fixed, decalcified,
paraffin sections from patients between the ages of 16 and 48 years. With one exception (a small cell
osteosarcoma), none of the lesions was
cytokeratin positive. Moreover, none of the lesions was
epithelial membrane antigen,
desmin,
factor VIII-related antigen,
synaptophysin, or Leu-M1 positive. Accordingly, strong positivity for these
antibodies in a majority of
tumor cells should prompt inclusion of
tumor types other than those listed above in the differential diagnosis.
Vimentin positivity was seen in a majority of the
tumors studied irrespective of histologic type. Scattered
tumor cells (< 25%) showed positivity with
antibodies to muscle-specific actin and smooth muscle actin in several of the different
tumor types studied. No lesions other than
lymphoma were
leukocyte-common antigen (LCA) positive; all but two
lymphomas were LCA positive, while all but one
lymphoma were L26 positive. One (
lymphoblastic) lymphoma was LCA and L26 negative. S-100,
neuron-specific enolase, and Leu-7 did not prove to be specific for "neural-associated"
tumors, but rather appeared in some small cell
osteosarcomas, Ewing's
sarcomas, atypical Ewing's
sarcomas,
primitive neuroectodermal tumors,
mesenchymal chondrosarcomas,
lymphomas, and Askin
tumors. Antibody to
cell surface antigen HBA71 was positive in three Ewing's
sarcomas (two typical and one atypical) and negative in small cell
osteosarcoma (three cases),
mesenchymal chondrosarcoma (two cases), and
lymphoma (one case). While some guidance may be derived from analysis of immunohistochemical staining patterns in a given lesion, the results reported in the present study do not suggest that routine immunohistochemistry alone will permit distinction of these small cell
tumors of bone from one another. The value of immunohistochemical studies appears to lie particularly in the use of
antibodies to LCA and
S-100 protein to distinguish
lymphoma and
mesenchymal chondrosarcoma, and perhaps antibody to HBA71 to distinguish neural family lesions (such as
Ewing's sarcoma), from other small cell
tumors, such as small cell
osteosarcoma.