Immunocytochemical characteristics of small cell lung carcinoma associated with the Lambert-Eaton myasthenic syndrome.

The Lambert-Eaton myasthenic syndrome (LEMS) is characterized by the presence of IgG antibodies to motor nerve terminals, and associates with small cell lung carcinoma in more than 60% of cases. We have carried out a comparative immunocytochemical study on small cell lung carcinoma (SCLC) in five LEMS cases and six non-LEMS cases, using antibodies to tumor markers, MHC Class I and II, macrophages and lymphocytes. The authors found a reduced expression of the 200Kd neurofilament antigen and of MHC Class I antigens in the LEMS cases as well as a greater infiltration of activated macrophages. It is suggested that these findings are consistent with the view that SCLC antigenic determinants trigger the autoantibody response in SCLC-LEMS.