A retrospective study was undertaken of local, regional, and distant recurrences in 346 patients with primary melanomas of tumor thickness less than 1.0 mm that were excised with margins of normal skin varying between 0.1 cm and 5.0 cm or more. Prospective histopathologic examination of 284 melanomas for the presence of microsatellites was also performed and their effect upon the frequency of local recurrence was studied. Margins of excision did not influence the frequency of local, regional, or distant metastases. Four recurrences of in situ superficial spreading melanoma occurred, however, when very narrow margins of excision (0.5 cm or less) were employed. Microsatellites were uncommon with tumors less than 3.0 mm in thickness (2.8% of all tumors of less than 3.0 mm in thickness, taken together), but relatively frequent in association with thicker tumors (37%). Melanomas with microsatellites were associated with a greater frequency of local clinical metastasis than those without (14% vs. 3%). Removal of more than 1.0 cm of normal skin around a melanoma of less than 1.0 mm in thickness does not further reduce rates of recurrence of any type. The use of margins of 0.5 cm or less for melanomas with a radial growth phase does appear to result in an increased frequency of local recurrence of the primary melanoma with an epidermal in situ component. These recurrences can be prevented by the removal of 1.0 cm of normal skin around such a melanoma. Microsatellites constitute a risk factor for local recurrence, but are a relatively uncommon phenomenon at tumor thickness less than 3.0 mm.

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Localized segments of the abdominal aortas of 18 dogs were irradiated with 50-kv. x-rays in doses ranging from 1,500 to 5,500 r (at the ventral surface of the aorta), and were examined histologically at intervals ranging from 2 to 48 weeks after irradiation. Arteriosclerosis developed at the irradiated sites and was significantly more severe than that which occurred in nonirradiated control sites in the abdominal aorta. There was evidence that severity of arteriosclerosis increased with time following irradiation of the aorta. There was less pronounced arteriosclerosis after 3,000 to 5,500 r than after 1,500 to 2,500 r. It appeared that the larger doses of x-rays inhibited the full development of the late lesions, although presumably causing more initial primary damage. X-irradiation appeared to be followed by the development of arteriosclerotic lesions similar to those that occur naturally in old dogs. It is proposed that irradiation may selectively cause injury of the internal elastic membrane, and that this degenerative phenomenon is followed by the development of intimal fibrosis and plaque formation.