Detection of bone marrow metastases in small cell lung cancer patients. Comparison of immunologic and morphologic methods.

An immunocytochemical method, involving four monoclonal antibodies (MAbs) previously selected for their specific binding to small cell lung cancer (SCLC) cells in human bone marrow, was used for detection of bone marrow metastases in 81 patients with diagnosed SCLC. This procedure was compared with two routine morphologic methods with regard to diagnostic efficiency and sensitivity. Bone marrow involvement was found in 26 patients (32%), one of which had limited disease according to conventional clinical criteria. Eight of the positive cases were exclusively diagnosed by immunocytochemistry, whereas the histologic and cytologic methods separately identified two patients each. Immunocytochemistry had a detection level of tumor cells in the mononuclear cell fraction of approximately 1-2%, whereas no patients with less than 10% immunocytologically detectable tumor cells were diagnosed by cytomorphologic examination of bone marrow aspirates. Evidence was obtained that the diagnostic efficiency of any method increased with the number of samples examined. Of the four MAbs used, the anti-NCAM antibody, MOC-1, labeled tumor cells in all immunologically positive patients, and in all but one of these patients all cytologically confirmed tumor cells were stained. The antibodies MOC-31, which recognize a cluster-2 antigen, and NrLu10 bound nearly all tumor cells in most cases, whereas MLuC1 only diagnosed tumor cells in a fraction of the patients. The results show that the immunocytochemical application of these antibodies is superior to morphologic techniques in detecting SCLC bone marrow metastases. Further use of the method might provide prognostically and therapeutically useful information.