Melanoma

MELANOMA (melanoma), a tumor arising from tissue that produces the pigment melanin. Such tissue, as is known, is located in the epidermis (melanoblasts, melanocytes), the coats of the eye, and the coats of the brain and spinal cord. As a result of a developmental defect, it may also be found in other parts of the body. The benign form of M. should be considered to be the pigmented nevus (naevus pigmentosus—see Naevus). Pigmented nevi may undergo malignant transformation and become the starting point of malignant M. This is the most common pathway of occurrence of the latter. Often such M. also arise from the pigmented coat of the eye, less often directly from the skin, mucous membranes (vulva, rectum), or the coats of the brain. (The possibility of primary occurrence of M. from the adrenal gland is extremely problematic.) Depending on the amount of pigment (intensity of pigment formation), malignant M. is gray, brown, or completely black. The production of pigment is an indicator of the maturity of the tumor elements: the younger they are, the less pigment they produce, and the lighter the tumor. Completely immature M. can even be white. In pigmented (melanotic) forms, melanin, which has a yellow-brown color, is contained in the protoplasm of cells either in the form of small granules or in the form of large clumps. Sometimes the amount of pigment produced is extremely large, leading to pigment transformation of cells. Necrosis, melting, and hemorrhage are frequent phenomena in M. Hemorrhages lead to the formation of hemosiderin, which can be absorbed by the tumor cell, so that two different pigments may be present in it at the same time. Melanin is also regularly encountered in the stroma of the tumor. It gets there in the order of resorption and represents a phenomenon of pigment transfer. According to its histological structure, most M. appears either as a collection of large round cells resembling epithelial cells arranged in nests among a scant but clearly distinguishable stroma, or consists of spindle-shaped, elongated, and branching elements resembling chromatophores. In the first case the tumor has an "alveolar" structure and resembles cancer; in the second it resembles a spindle sarcoma. Malignant M. is distinguished by extremely rapid progression and gives extensive metastases, spreading primarily by the blood route. In some cases all organs (especially the liver) and the skeleton may contain countless small and large colored or colorless nodes of new growth. In rare cases in this situation (and sometimes even in the absence of metastases) a general melanosis (see) is observed, accompanied by melanuria. As to what type of tumor—epithelial or connective tissue—malignant M. should be classified, i.e., whether it is a carcinoma or a sarcoma, this has not yet been finally clarified. One thing is certain, that there are separate M. originating from the epidermis and having the clear structure of squamous (even keratinizing!) carcinomas; in other words, it is certain that part of M. are undoubtedly melanocarcinomas. As for M. originating in the corium from nests of so-called Naevuszellen, their histogenesis must be considered unclear insofar as the histogenesis of the Naevuszellen themselves is unclear. If, together with Unna and Lubarsch, one considers them epithelial elements, then the tumors originating from them logically must be recognized as cancers; if, however, Naevuszellen are considered connective tissue elements, then M. arising from them should be recognized as melanosarcomas. In view of the fact that some M. consist predominantly of elongated and branching forms (chromatophores) also containing melanin, Ribbert, who admits an independent pigment-forming function of chromatophores, proposes to call all melanotic tumors chromatophoromas. In view of the uncertainty of the question at the present time, it has been proposed to designate all malignant melanotic tumors by the neutral name "melanoma," "melanoblastoma," or "melanocytoblastoma," which defines only that the tumor originates from pigment-forming tissue regardless of its genetic nature. The mentioned names, especially the first two, have now acquired full citizenship. M. also occurs in animals, especially frequently in white horses. The place of primary occurrence in them is muscle, lymph, glands, heart, lungs, parotid glands; in sheep also the skeletal system. As for cats and dogs, in them M. originate primarily on the skin and on the eyes. According to comparative statistical data of Lubarsch at the Berlin Veterinary Institute for 1896/97–1910/11, in 175,745 horses 527 cases of malignant formations were detected, of which 42.88% turned out to be malignant M., whereas in 143,309 dogs 865 carcinomas and sarcomas corresponded to only 3 melanomas, i.e., 0.35% of all malignant tumors. The frequency of M. in humans according to Lubarsch's statistics for 1906–1919 reaches 20 cases per 18,113 autopsies, i.e., 0.89% of all malignant new growths, of which there were 2,274. According to the same statistics, the greatest number of cases in horses falls on older age; in humans under 30 years of age there were 4 cases, in the period 30–82 years—16 cases. The etiology of malignant M. is connected with the theory of the origin of tumors in general. Therapy is problematic. Timely surgical removal (enucleation of the eye) can sometimes give recovery; however, one must always bear in mind the possibility of late (several years later) recurrences and late manifestations of metastases.