The pattern of the mononuclear infiltrate as a prognostic parameter in flat superficial spreading melanomas.

The mononuclear cell infiltrate of 90 superficial spreading melanomas (SSM) of less than or equal to 1.5 mm thickness was analyzed at different locations around and within the tumors. All patients had been followed for at least 5 years, and 20 (22%) had developed metastases. A correlation between the overall inflammatory response in the histologic sections and the prognosis was not observed, nor could a significant distinction be made between metastasizing and nonmetastasizing melanomas when the mononuclear cell infiltrate was analyzed at different locations. A significant clustering of metastasizing tumors was, however, observed in the subgroup with a relatively strong infiltrate within the tumor compared with the overall infiltrate. From this observation, a semiquantitative description of the pattern of the infiltrate was established. It provides an additional parameter for prognostication in flat SSMs and it raises new questions about the role of the local host-tumor interaction.