Occult melanoma in lymph nodes detected by antiserum to S-100 protein.

Sections of 1,273 nodes from 58 patients with melanoma were stained in an immunoperoxidase assay using an antiserum to S-100 protein and aminoethyl carbazole as indicator. By the hematoxylin and eosin (H. and E.) technique, 128 nodes were seen to contain melanoma (10%); by the anti-S-100 protein technique, 363 (29%) were found to be tumor-positive. The additional tumor-positive nodes contained single tumor cells or small groups of tumor cells and were adjacent to nodes that were partly or wholly replaced by melanoma. Penetration of nodes by single tumor cells was seldom seen in node groups containing no tumor that was visible on H. and E. staining. The anti-S-100 protein approach more accurately identified those patients who would die of their recurrent disease less than 5 years after lymphadectomy.