Melanomas

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Abstract
The term melanoma embraces a group of tumors which are characterized by the formation of melanin. The benign form is known as the pigmented nevus, and the malignant form as melanosarcoma, melanocarcinoma, or malignant melanoma. The benign melanoma, which is often present at birth, may occur anywhere on the surface of the body, in the mucous membranes of the upper and lower ends of the digestive tube, and in the eye. In a majority of instances it gradually becomes fibrosed and remains quiescent throughout life. In an occasional case, however, it undergoes malignant proliferation to produce a histological picture that may resemble neurogenic sarcoma, epidermoid carcinoma, or anaplastic malignancy. It may then spread, by way of the lymphatics or by the blood stream, to various locations in the body, to set up secondary growths. Pigment formation may or may not occur in these secondary lesions. Melanin Formation: The pigment in melanotic tumors has been attributed to various sources. It was first thought to be derived from hemoglobin, but it is now known that when iron pigment is present in these tumors, it is secondary to extravasations of blood. Others have considered it a product of nuclear or nucleolar activity, regarding the pigment as chromatin granules extruded from the nucleus of the cell. The idea that melanin formation was the result of an oxidation process was first suggested by Thormählen, quoted by Spencer, who observed that the urine of a patient suffering from secondary melanotic sarcoma of the liver turned dark on exposure to air and became increasingly dark by the addition of oxidizing agents. Quattini, also quoted by Spencer, arrived at a similar conclusion from his experiments on rabbits. He injected pyrrole, skatole and indole subcutaneously and noted, in nine to eighteen days, a darkening of the skin of the animals in spots, accompanied by an increased growth of pigmented hair. These experiments, he believed, indicated the presence of a ferment in the epidermal cells which had acted upon a colorless chromogenic substance related to the indole groups, to produce melanin. Bloch then carried out staining experiments on frozen sections, using various members of the aromatic series. He found that a 1 per cent aqueous solution of 3:4-dihydroxyphenylalanin (contracted to dopa) was oxidized by a specific ferment present in certain cells of the epidermis and hairs, with the production of a brown pigment, but he was unable to obtain a similar result with any other substance. He found, however, that of the other pyrocatechol derivatives, adrenalin, in the presence of abundant oxydase turned the hairs brown, though it had no effect upon the basal cells of the epidermis. From his experiments Bloch concluded that the formation of melanin was brought about by the oxidation of a colorless chromogenic substance. This substance he believed was chemically closely allied to 3:4-dihydroxyphenylalanin (dopa) and adrenalin, and was present in the blood plasma. The oxidation was brought about by means of a specific ferment (dopa-oxydase) produced in certain cells of the epidermis and its derivatives. These cells he designated as the true melanoblasts.

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