Specificity: This antibody is reactive 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 in April 1987. MOC-31 reacts with most epithelia, and, in lung cancer, all lung carcinomas. The membrane-associated proteins detected by MOC-31 appear to have an apparent molecular weight of 35-40 kD. MOC-31 is not reactive with normal and malignant mesothelia and therefore is especially useful for the detection of carcinoma cells in ascites or pleural effusions (4).