Melanocytic cutaneous lesions and melanotic regional lymph nodes in slaughter swine

During a five month period, 220 slaughter swine (at two abattoirs) had gross cutaneous and lymph node lesions suggestive of melanoma. Lymph nodes from 214 and cutaneous lesions from 176 of these pigs were submitted for histological examination. Of the cutaneous lesions, 174 were spontaneously regressing melanomas, and two were nonregressing. Regression usually commenced by infiltration of the lesion by lymphocytes, plasma cells and the formation of giant cells. Of the melanotic lymph nodes, 177 were diagnosed as melanosis, 35 were considered to be metastatic regressing melanomas, and two were nonregressing melanomas. This report indicates a high rate of spontaneous regression in swine melanomas detected at slaughter.