Melanoma cell heterogeneity. A study of two monoclonal antibodies compared with s‐100 protein in paraffin sections

: Fifty-six formalin, Bouin's, and Carnoy's fixed, paraffin-embedded malignant melanomas (21 primary, 35 secondary), were studied by avidin-biotin complex immunohistochemistry using monoclonal antibodies (MoAb) HMB-45 and B1.1, comparing reactivity with polyclonal anti-S-100 protein. B1.1 (anti-CEA MoAb) was expressed in a minor percentage of cells of the invasive component of some primary melanomas, and weak to moderately in scattered metastic melanoma cells. MoAb HMB-45 prepared against melanocytic tumors reacted with over 90% of all tumors studied, being weakly reactive in one, and nonreactive in four metastases. This antibody stained some primary melanomas and their dysplastic nevus components in a heterogeneous manner, but was largely nonreactive in deep dermal nevus cells that were in association with invasive melanoma, enabling recognition of the deepest penetration of melanoma cells in the dermal nevus component. MoAb HMB-45 appears specific for melanoma cells, with no cross-reactivity with nonnevomelanocytic malignant tumors (unlike polyclonal anti-S-100 protein). MoAb HMB-45 is more sensitive in detecting malignant melanoma cell heterogeneity than anti-S-100 protein.