Analysis of soluble melanoma cell membrane antigens in metastatic cells of various organs and further studies of antigens present in primary melanoma.

In malignant melanoma, using Sephadex G-200 chromatography and polyacrylamide gel electrophoresis (PAGE), it has been possible to separate two types of skin reactive antigens. The first, found in Sephadex fraction II and PAGE region a appears specific for melanoma. Allogeneic extracts have produced positive reactions in many patients with skin or ocular melanoma, and have given negative reactions in patients with other types of cancer or in patients with ocular lesions simulating melanoma. The second group of antigens, in Sephadex fraction III and PAGE region b were less specific. These antigens produced positive skin reactions in some patients with breast cancer, as well as in patients with melanoma. Reactivity to PAGE region a appeared to be confined to one protein band, but three different bands in region b gave positive reactions. A study was made of the presence or absence of similar antigens in metastatic deposits of malignant melanoma. Metastatic lesions in the following tissues were analyzed: liver, lung, adrenal, skin, and colon. These were compared with pooled primary skin melanomas by skin testing in the same patients. The tumor-associated melanoma antigen, found in Sephadex fraction II and PAGE region a appeared to be strongest in adrenal, lung, and liver metastases. It was found that the protein yield in this region was not indicative of the strength of the antigen. Therefore, a careful, detailed analysis of the protein bands present in PAGE regions a and b from primary skin melanoma was conducted. Only one band in PAGE region a was found to be responsible for positive skin reactivity. This band was found to be a glycolipoprotein. Further studies were also conducted in order to determine whether or not some of the antigens present might be fetal antigens. Some of the protein bands present in Sephadex fraction III and PAGE region b of melanoma appeared to be similar to some of the PAGE region b proteins present in fetal skin cells. Two bands from fetal skin also had the same location on PAGE as two bands from ductal breast cancer, although the relationship to melanoma region b antigens was not exact. These fetal proteins, which seemed to be present both in ductal breast cancer cell membranes and in melanoma cell membranes, might account for the positive skin reactivity seen in this region, and also for the cross reactivity of skin tests with this antigen.