Detection of bone marrow metastasis in small-cell lung cancer by monoclonal antibody.

A murine monoclonal antibody against a surface antigen of small-cell carcinoma of the lung (SM1 antibody) was investigated for its use in detecting bone marrow metastasis. Bone marrow cells of healthy volunteers and of patients with small-cell carcinoma of the lung (SCCL) were examined for reactivity with SM1 antibody and indirect immunofluorescence and the results compared to conventional histochemical staining (Wright-Giemsa stain of bone marrow aspirates and hematoxylin-eosin stains of bone marrow biopsies). No SM1 reactivity was found in marrow cells of eight healthy volunteers. Thirty-six samples from 33 patients with SCCL were examined; tumor involvement was found in 69% by SM1 antibody and in 16% by histochemical stains. All bone marrow samples from patients with SCCL that were unreactive with SM1 antibody also showed no evidence of tumor involvement by histochemical stains. Samples of 29 patients were investigated at initial staging; SM1 reactive cells were found in 50% of 16 patients with limited disease and in 77% of 13 patients with extensive disease. Overall, the proportion of patients recognized to have disseminated disease at diagnosis was increased from 45% to 72% by monoclonal antibody staining. Indirect immunofluorescence with SM1 antibody allows detection of bone marrow metastasis of SCCL that cannot be seen by conventional morphology and can identify disseminated disease in patients otherwise staged limited disease.