Paucity of beta 2-microglobulin expression on small cell lung cancer, bronchial carcinoids and certain other neuroendocrine tumors.

Cell lines established from small cell lung cancer (SCLC), a neuroendocrine tumor, have low or absent expression of class I major histocompatibility complex antigens. To determine whether this phenomenon occurs also in vivo, 244 routine paraffin-embedded tumors including 32 SCLC and 79 non-SCLC (NSCLC) lung cancers were studied for expression of beta 2-microglobulin (beta 2m) by an avidin-biotin coupled immunoperoxidase technique. The majority of SCLC tumors lacked beta 2m expression, while some had weak, focal expression. In contrast, most NSCLC expressed beta 2m, often strongly. The difference between SCLC and NSCLC was highly significant statistically, suggesting that beta 2m can be used as a clinical immunodiagnostic marker for distinguishing NSCLC from SCLC. In addition, certain other neuroendocrine tumors (neuroblastoma, bronchial and midgut carcinoid tumors) lacked beta 2m expression, whereas some (pheochromocytoma, medullary thyroid carcinoma, and peripheral neuroectodermal tumors) usually stained positively. Such non-neuroendocrine tumors as colon, breast, and prostate carcinomas showed moderate to high expression of beta 2m. Selective absence of beta 2m expression by certain neuroendocrine tumors appears to be a phenomenon of biological and diagnostic importance.