Small cell lung carcinoma is distinctive from other kinds of lung cancer (metastases are already present at the time of discovery) and accounts for approximately 110,000 cancer diagnoses annually. This antibody reacts with lung cancer associated antigens and has been studied and categorized in different clusters of reactivity patterns during the First International Workshop on Small Cell Lung Cancer Antigens held in London, England in April 1987. It reacts with most epithelia and, in lung cancer, all lung carcinomas. The membrane-associated proteins detected appear to have an apparent MW of 35-40 kD. It is unreactive with normal and malignant mesothelia.