Cryostat sections of 19 squamous cell carcinomas, 13 keratoacanthomas, and 12 papillomas, induced by 7,12-dimethylbenz(a)anthracene in the skin of rabbits and rats were examined by indirect immunofluorescence with human serum containing antibody to smooth muscle. Linear or granular staining of the cell outlines of the basal squamous cell layers was seen most extensively in the carcinomas, less in keratoacanthomas, and least in papillomas. In addition, squamous cell carcinomas showed this pattern of staining at advancing tumor margins and in invasive cords and tumor cell nests in the dermis. Four keratoacanthomas also showed prominent staining of the basement membrane area. The specificity of the staining reaction was established by its prevention on neutralization absorptions of the serum with extracts or homogenates of smooth muscle. The epidermal cells of normal rabbit and rat skin gave negative staining reactions. The presence of smooth muscle-associated antigen probably corresponds to cellular microfilaments.

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This work was supported by grants from the Anti-Cancer Council of Victoria and the National Health and Medical Research Council.

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