Monocytes and macrophages in malignant melanoma. I. Peripheral blood macrophage precursors

A micro-assay designed to assess the capacity of peripheral blood mononuclear cells to differentiate in vitro into mature macrophages is described. In patients with "final common pathway" malignant melanoma, there was a highly significant deficiency in macrophage precursors (MPs). By conventional morphological criteria such patients did not show a significant monocytopenia. Serum factors do not seem to contribute to the MP defect in the patients. We conclude that these patients have an intrinsic functional defect in their peripheral blood monocytes, but the mechanisms responsible for this defect are as yet unknown.