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Dermatopathology: Practical & Conceptual April - June 2008
5. New Heights: “Animal-type” melanoma and entities related to it (Part I): Evolution of a concept
François Milette, M.D.
A. Bernard Ackerman, M.D.
Contents of Part I
I. Melanosis in horses and men? (Dick, 1832)
II. A précis of equine melanotic disease (Levene, 1971)
III. Melanoma arising in “blue nevi”? (Darier, 1925)
IV. Diffuse mesodermal pigmentation? (Carleton and Biggs, 1948)
V. Melanotic disorders in horses and men? (Levene, 1979)
VI. Pilar neurocristic hamartoma? (Tuthill, Clark, and Levene, 1982)
VII. Malignant melanoma arising in a blue nevus? (Pathy, Helm, Elston, Bergfeld and Tuthill, 1993)
VIII. Cutaneous malignant melanotic neurocristic tumor arising in neurocristic hamartoma? (Pearson, Weiss, Headington, 1996)
IX. Malignant melanoma with prominent pigment synthesis: “Animal-type melanoma”? (Crowson, Magro, Mihm, 1999)
X. Animal type melanoma? (Requena, de la Cruz, Moreno, Sangueza, Requena, 2001)
XI. Animal-type melanoma? (Kazakov, Rütten, Kempf, Michal, 2004)
XII. In the textbooks?
XIII. Melanomas in horses as described in veterinary medicine literature? (Valentine, 1995; Seltenhammer, 2004)
A catalogue of terms pertinent to this endeavor, in alphabetical order.
—Animal-type melanoma with balloon-cell change
—Cellular blue nevus with massive lymph node metastase.
—Cutaneous malignant melanotic neurocristic tumors arising in neurocristic hamartoma. A melanocytic tumor morphologically and biologically distinct from common melanoma
—Congenital and infantile melanoma: an uncommon pigment synthesizing variant
—Equine melanotic disease
—Equine/animal-type melanoma in humans: malignant melanoma with prominent pigment synthesis
—Malignant melanoma arising in a blue nevus with features of pilar neurocristic hamartoma
—Malignant melanoma with prominent pigment synthesis: "animal-type melanoma"
—Melanoma associated with blue nevus and melanoma mimicking blue nevus: on the spectrum of "malignant blue nevus"
—Mesenchymal malignant melanoma or melanosarcoma
—Metastatic melanomas of the skin mimicking blue nevus
—Nodal and subcutaneous cellular blue nevus. A pseudometastasizing pseudomelanoma.
—Pigmented epithelioid melanocytoma: a low-grade melanoma with metastatic potential indistinguishable from epithelioid blue nevus and "animal-type" melanoma
—Pigment synthesizing melanocytic tumor: a low-grade melanoma with frequent lymph node metastasis
—Pigment synthesizing melanoma: a low-grade melanoma with marked resemblance with epithelioid blue nevus
—Pilar neurocristic hamartoma: its relationship to blue nevus and equine melanotic disease
Even though oxymorons and concepts illogical abound in general pathology and in dermatopathology, the fusillade of them pertinent to the concept of "animal-type melanoma" (animal-type melanoma) is dazzling. To the list formidable above must be added the recently described "amelanotic blue nevus," i.e., "a not blue nevus" which presages a yet to be presented "amelanotic malignant blue nevus," i.e., "a not blue malignant nevus"!
In short, although the notion of animal type melanoma is dizzying, more and more articles are being devoted to it. The reason for that might be simpler than at first it seems. All of the terms that grace the list above, as well as "dysplasia" before them, are camouflage for not knowing the answer to a particular question and anxiety that proceeds from that state of uncertainty which is the situation of a histopathologist who cannot give a diagnosis specific for a "difficult case." Sad to say, the welter of terms and the ideas wooly that animate them actually reinforce ignorance and impair generation of new knowledge which, paradoxically, is the only antidote for it. Our goal here is to bring comprehension clear as crystal to the matter of "heavily pigmented melanocytic lesions," in particular, so-called animal-type melanoma and the entities said to be related closely to it, among those being "epithelioid blue nevus" and "pigmented epithelioid melanocytoma," to say nothing of dermal melanosis.
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