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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)
V. Melanotic disorders in horses and men? (Levene, 1979)
In 1979, Levene catalogued findings of the autopsy he had performed in 1975 [
] of the condition peculiar in the patient first reported on in 1948 by Carleton and Biggs under the title "disseminated melanosis." [
] The changes must have been riveting to Levene because in many ways they were comparable to the observations he had made in his thesis devoted to equine melanotic disease published in 1971. [
The patient, who was the very same person reported on by Carleton and Biggs in 1931, then age 14 at the time of presentation initial, died at 43. The cause of her death was deemed by Levene to be metastatic melanoma. At autopsy, pigmented masses were found in lymph nodes and in the liver, whereas lesions more discrete were present throughout almost every organ.
The changes at examination postmortem were summarized by Levene in these four passages telegraphic:
"Widespread melanosis of melanocytic and mixed melanocytic/melanophagic type.
Widespread melanosis, apparently a phenomenon of storage of melanophages, no melanocytes evident in the vicinity being a source of the melanin.
Terminal melanoma involving lymph nodes and liver mainly, but with no primary site discovered.
A cranial deformity unrelated to the problem pigmentary."
Levene made the comments following by way of explanation of the findings perplexing to him:
"A bluish gray nevus rarely encountered is congenital and of large dimensions, a variant of bathing trunk nevus, composed principally of intradermal nevus cells. The tumors undergo malignant change and it may be speculated that one of the skin blemishes in the present case was an occult melanoma. If so, it regressed spontaneously. The only naturally occurring condition with which it can be compared is equine melanotic disease . . . So great is the presence of melanophagia that the impression is that of a storage phenomenon akin to Gaucher disease rather than neoplasia."
In brief, for Levene the lesions present since birth were variants of a congenital nevus and in it a melanoma developed and eventually metastasized.
The extensiveness of "melanophagia" in all organs was so impressive to Levene that he compared it to a storage disease, such as that of Gaucher. According to Levene, the cells pigmented deeply in most of the deposits were different, as assessed by studies ultrastructural, from the cells of the melanoma itself, but no criteria precise for distinguishing the different types of cells were put forward by him. The study by Levene was the first in which investigations by electron microscopy were performed and, in preparation for what is to come, it must be yet emphasized that no mention was made by him of schwannian differentiation to which other authors later gave so much importance. Consistent as he was, Levene [
] underlined how closely the condition he reported on resembled equine melanotic disease, giving short shift to differences between the two conditions in a single sentence terse:
"The differences—absence of both early graying of hair and the formation of dermal melanocytic nodules in the human cases—are inexplicable species differences."
The occurrence terminal of "frank malignancy" (whatever that means) was explained by Levene in two different ways thus:
"1) It is reasonable to believe that malignant change occurs in the disseminated melanocytes.
2) It is possible that in both [humans and animals] there is an anomalous visceral distribution of melanocytes which in the majority of grey horses does no more than slowly produce melanin which is stored locally. Malignancy supervening would result in a primary visceral melanoma of heterotopic melanocytes."
Both of Levene's postulates are couched in language daunting to comprehension readily, even for one whose native language is English (Levene, himself, being an Englishman). For Levene, all of this indicated that
"Both human and equine disorders are related to benign metastasizing blue nevus."
In sum, for Levene, the lesion under consideration by him was a benign metastasizing blue nevus until it killed the patient, at which time it became a malignant blue nevus. For him, the death of the patient was the criterion ultimate for establishing the diagnosis.
For us, two things are certain about the patient reported on by Levene, they being these:
The patient died of metastatic melanoma.
At no time did she have either "benign metastatic" or "malignant" blue nevus.
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