Prediction of lymph node metastases from the histologic features of primary cutaneous malignant melanomas.

Elective regional lymph-node dissection was performed on 98 patients with clinical Stage I cutaneous malignant melanoma and 26 of them were found to have microscopic evidence of metastases. The histology of the primary lesions was reviewed in order to find possible prognostic parameters that would allow prediction of nodal involvement. There was an increased risk of occult lymph node metastases with increasing thickness of the primary lesions. While this trend was not found to be statistically significant, no occult lymph node metastases were found for lesions less than 1.0 mm in thickness. Significant features included mitotic figures, "prognostic index," and plasma cells within the infiltrate. A multiple logistic regression analysis identified three groups of patients with low, medium, and high risk of occult metastases, based on thickness, location, and plasma cells. The correlation between plasma cells and the incidence of metastases in lymph nodes might represent an immunologic phenomenon.