In vitro clonal assay for human metastatic melanoma cells.

An in vitro assay for clonogenic tumor cells was applied to human metastatic melanomas. Melanoma colony formation was observed in 22 of 33 samples obtained from a variety of involved tissues. The melanocytic tumor origin of colonies was established by serial observations by inverted light microscopy, staining of fixed colonies for melanin, and cytological and karyotypic analysis of cells within colonies. Two morphologically distinct types of colonies were identified, one consisting of light large cells and the second of dark small cells. Investigations of factors which modulate growth and differentiation of clonogenic melanoma cells may provide a clearer understanding of this neoplasm.