In the normal lung, a subset of cells with a histological appearance consistent with that of Kulchitski cells are the only lung cells reacting with a monoclonal antibody (MOC-1) raised against a human small cell lung carcinoma-derived cell line. Outside the lung, a subset of normal endocrine cells (in the adrenal, thyroid, ovary, and pancreas) as well as neural cells (brain and peripheral Schwann cells) also express the antigen detected by MOC-1 (named MOC-1-related antigen). Some of these positively reacting cells are ectodermally derived, whereas others are of proven endodermal origin, indicating that the MOC-1-related antigen is not a cell lineage-specific antigen. Instead, the common expression of the antigen by cells with a neural, endocrine, or neuroendocrine function suggests that the antigen relates to a neuroendocrine differentiation state of these cells.

The presence of the MOC-1-related antigen on several nonlung tumors mostly paralleled its normal tissue distribution, indicating that the antigen is generally retained upon malignant transformation. In lung carcinoma, the antigen proves to be present on almost all small cell carcinomas tested. In addition, adenocarcinoma and mixed adenosquamous carcinoma could also express the antigen, whereas pure squamous cell carcinoma generally did not. This finding will be discussed in relation to a proposed “common stem cell” histogenesis of lung carcinoma.

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This investigation was supported by a grant (GUKC 82-6) from the Netherlands Cancer Foundation (Koningin Wilhelmina Fonds).

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