That melanomas in horses and other animals is not defined or understood better than in man is testified to by the quotations following culled from a retrospective study by Valentine of "equine melanocytic tumors" in 53 horses:

"Melanocytic tumors in horses are described as slow growing, locally invasive tumors that frequently result in metastasis." [20]

Melanocytic tumors in this instance is meant to be melanomas BUT "Four different kinds of equine melanocytic tumors [exist]: melanocytic nevus (melanocytoma), dermal melanoma, dermal melanomatosis and anaplastic melanoma." [20]

This curious classification is then commented on in a manner dizzying because of contradictions inherent in it: "[some] tumors were classified as melanocytic nevi (melanocytomas) . . . One tumor classified as melanocytic nevus was invasive . . . Five discrete [dermal] melanomas . . . were considered benign."

"Dermal melanoma and dermal melanomatosis are generally indistinguishable and are differentiated by their clinical features (i.e., number of tumors, confluence of them and outcome) . . ." Later in the same article comes this eye-opener: "In dermal melanomatosis surgical excision is not feasible and internal metastasis were found in 6 horses at necropsy." The last sentence compels to the conclusion that "dermal" melanomatosis not only is "dermal," but metastatic widely.

Whereas histopathologically "animal-type" melanoma or "equine-type" melanoma is described generally as typified by confluent plaques of cells, absence of mitotic figures, and presence of melanin in amount extraordinary, yet another type of melanoma in horses, i.e., one anaplastic, is said to be characterized by "highly pleomorphic, variably pigmented, presenting numerous mitosis and widespread single-cell invasion of epidermis." The term "human-type melanoma" seems altogether fitting for these lesions in "lower" animals!

It is understandable readily why the authors of the review just cited [20,22] wrote that "As in many species, it is clear that the differentiation between benign and malignant equine melanocytic tumors can be difficult." [20] No criteria clear, crisp and solid are provided, ever, for enabling differentiation histopathologic between the benign and the malignant melanocytic tumors in horses. That being so a histopathologist attempting to distinguish one from the other is clueless and rudderless.

That the concepts of "equine melanocytic tumors," "neurocristic hamartomas," and "animal-type melanomas" are flawed irrevocably is made apparent, too, by the potpourri of titles given to articles that pertain to the subject of deeply pigmented lesions of melanocytes, both in "lower" animals and in humans animals, they being enumerated in a list that reposes at the very beginning of this monograph.

Some authors seem to agree with our position and proposition but for reasons diametric to our own. Recently, it has been suggested that the designation "animal-type melanoma" be replaced by still another term for designating generically all "heavily pigmented" melanocytic tumors, namely, "pigmented epithelioid melanocytoma." [2] That subject imponderable deserves analysis critical and that is what we endeavor to undertake in Part Two of this Arbeit.