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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)
XII. In the textbooks?
How is "animal-type melanoma" treated in textbooks of dermatopathology? The following, from different texts current, are quotations verbatim that pertain to the matter of "animal-type melanoma":
Lever's Histopathology of the Skin,
"animal-type" melanoma ("macrophagic melanoma"): Behavior of these lesions is unpredictable . . ."
Just a few lines later, a rectification subtle to this assessment is added in "Lever" as follows:
". . . biological behavior [is] difficult to predict on morphologic grounds."
"Animal type (equine type) melanoma is jet black in colour and composed of heavily pigmented epithelioid cells with numerous melanophages . . . In humans its behavior has been unpredictable."
Crowson, Magro and Mihm's
The Melanocytic Proliferations: A Comprehensive Textbook of Pigmented Lesions,
"The biological behavior of these heavily pigmented "animal-type" melanoma is unclear."
And elsewhere in the volume, the collaborators make this statement:
"The differential diagnosis [of animal-type melanoma] encompasses benign and cellular pigment-synthesizing melanocytic tumors."
McKee et al's
Pathology of the Skin with Clinical Correlations,
"Prognosis of this tumor is variable and systemic metastases with resultant death has been documented. It has been recommended that these tumors be treated as for classical melanoma."
No definition of "classical melanoma" is offered by McKee and coworkers. It cannot be emphasized too forcefully that none of the authors of any of these textbooks proposed criteria comprehensible and lucid for diagnosis of so-called animal-type melanoma, and neither did they do that for borderline melanoma, minimal deviation melanoma, and nevoid melanoma, fictions all. How sad and sorry a situation that is for a discipline, for students of it, and for patients.
Reading the quotations just excerpted, it becomes apparent that those who have written about the subject of "animal-type melanoma" are more concerned about considerations prognostic than with criteria diagnostic, a mentality that infused other notions nonsensical that emanate from one school of dermatopathologists whose home base originally was Harvard and then the University of Pennsylvania, among those being the reputed types of melanoma (lentigo maligna, superficial spreading, acral lentiginous and nodular) in Clark's so-called histogenetic classification and the folly of melanocytic dysplasia, which became the springboard for the "dysplastic nevus" and the "dysplastic nevus syndrome," they being the two examples egregious of many. But even the prognosis they seek to predict is said by them to be "unpredictable," "difficult to predict," "unclear," or "variable." For us, the reasons for that are clear, namely, "animal-type melanoma" is no less a fiction than the "histogenetic classification" and the "dysplastic nevus syndrome," to say nothing of melanomas characterized as "borderline" and "minimally deviant."
In short, all the textbooks consulted by us parrot, without any trace of mentality skeptical, assessment critical, or completeness encyclopedic, what has been published earlier in articles lacking equally in scholarship about the subject. What emerges is a concept deformed and useless, it thereby teaching nothing; it muddles, it obfuscates, it deadens. Only through a challenge direct, such as ours here, to a notion flawed irreparably, i.e., "animal-type melanoma" (but also to scores of analogues of it in the realm of melanocytic neoplasia, all of them malformed grotesquely), can a human brain maintain vitality and, at the same time, endeavor to preserve, and even enhance, aliveness of the cerebrum of colleagues.
Not only is the concept of "animal-type melanoma" useless because it is untenable, but never should it have been introduced in the first place, a charge that indicts reviewers of articles who recommended those manuscripts be accepted for publication in medical journals, and, even more, the editors of those journals who bear responsibility ultimate.
Let us summarize, briefly, why malarkey about "animal-type melanoma" never should have seen the light of day.
First and foremost, the term "animal-type melanoma" is an abomination linguistically; there is no such thing as "vegetable-type" or "mineral-type" melanoma, neither is any melanoma "animal-type" because man is an animal. Furthermore, a melanoma, itself, cannot be a type of animal; it is a type of neoplasm malignant. Parenthetically, the term "equine-type melanoma" is no better than "animal-type melanoma" and, in addition, is far too restrictive because lesions in all respects nearly identical to those described in horses have been encountered also in mice, in dogs, and in other "lower" animals.
Second, the term "animal-type melanoma" implies that melanomas occurring in animals (and particularly in horses) are entities both established and understood well with an appearance histopathologic recognizable with reliability by microscopists. That, too, is untrue. Melanomas in horses and other "animals," just as melanomas in human animals, are protean remarkably with variants innumerable in patterns architectural and in findings cytopathologic.
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