The frequency of CD4+ lymphocytes in dogs with melanoma in the present study was 43%, which was consistent with the prevalence in published studies of dogs with various types of cancer, in that the frequency of CD4+ ranged from 32 to 51% and did not differ markedly from the frequency in healthy dogs in these studies, which ranged from 35 to 38% (27–30). Here, CD4 is linked to melanoma.