Hematopoietic cell surface markers on metastatic small cell carcinoma detected with monoclonal antibodies.

Using a panel of monoclonal antibodies, cells from lymph node biopsies have been examined in three patients with small cell carcinoma presenting with cervical lymphadenopathy. Two patients had small (oat) cell carcinoma of the lung; in the third patient, a primary tumor was not found. Two lymph node biopsies showed typical small (oat) cell carcinoma, and one was an intermediate cell variant; in the last, lung biopsy showed small (oat) cell carcinoma. Electron microscopy demonstrated desmosomes in all three tumors. In each case, lymph node cell suspensions were examined by indirect immunofluorescence with the use of a panel of monoclonal antibodies to antigens usually associated with lymphoid or myeloid cells. In two of the three cases malignant cells were positive with the lymphoid marker BA-2; in two cases malignant cells were positive with OK1a1, a marker for the Ia-like antigen (HLA-DR); and in one case malignant cells were positive with My-1. Caution is needed in the interpretation of cell surface marker studies in the differential diagnosis of small round cell tumors.