To validate the supposition that thin malignant melanomas (less than 0.76 mm thick) of ordinarily low risk but with areas of regression may paradoxically metastasize, we observed 121 thin malignant melanomas over a six year period. Of these, 23 displayed readily apparent areas of regression, of which five (21.7%) metastasized. The incidence of metastases in their 98 counterparts without regression was 2.0% (2/98). The difference between the two is statistically significant (p = less than .01). Of the entire group of the two is statistically significant (p = less than .01). Of the entire group of thin melanomas, those with regression represented 19.0% (23/121) yet accounted for a disproportionate 71.4% (5/7) of all metastases. We conclude that regression is a relatively poor prognostic sign, whose occurrence within an otherwise thin melanoma represents a significant caveat to the current histologic staging system that equates thinness with low risk. We thus submit that patients whose malignant melanomas display regression be followed rigorously for evidence of metastases irrespective of the tumor's actual measured thickness or level of invasion.

Thirteen of 324 patients with malignant melanoma followed during a 24 month period experienced dissemination. The thorax was the initial site for relapse in 12, all of whom were asymptomatic. Ten gave no evidence of extrathoracic disease. Retrospective analysis of previous x-rays originally interpreted as negative revealed metastases in 33%. Life table analysis demonstrated a significantly longer survival for the subset with isolated intrathoracic metastases treated surgically than for their counterparts with metastases no longer amenable to surgery and treated by other modalities. We conclude that the thorax is the site of predilection for initial systemic relapse in malignant melanoma, that detection of early, surgically resectable metastases correlates with longer patient survival, and that routine chest roentgenography is inadequate in reliably uncovering such early disease. These data suggest the potential value of more vigorous radiographic surveillance (with either computed tomography or conventional full lung tomography) in patients at high risk for relapse.

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