Background: There is an increase in the incidence of cutaneous malignant melanoma (CMM) among white people throughout the world. In Sweden, a fivefold increase has been recorded since 1960, but the mortality is rising at a much lower rate. Tumor thickness is the single most important prognostic factor for primary melanoma. This study aimed to clarify whether the thickness of the tumor in invasive CMM decreased during the period 1965-1985.
Methods: This population-based study identified 574 cases of CMM, both invasive and noninvasive, in the South Swedish Health Care Region in 1965, 1975, and 1985. Twenty-six cases were excluded because the collection or evaluation of the material was not possible. The remaining 548 cases were reviewed histopathologically, and a diagnosis of invasive CMM was rejected in 71 cases. Eventually, 467 cases of invasive melanoma remained in our study (70 in 1965, 124 in 1975, and 273 in 1985). The level of invasion, tumor thickness, regression, ulceration, presence of inflammatory cells, benign naevus cells, and the site of presentation were studied.
Results: The study found neither a significant decrease of tumor thickness of invasive CMM nor changes in the level of invasion or proportion of ulcerated melanoma. A significantly higher proportion of melanoma tumors containing benign naevus cells was seen throughout the years (P < 0.05). Women had significantly fewer inflammatory cells in their tumors than did men (P < 0.01). As expected, the anatomical site of presentation showed a significant sex-related difference, with more tumors on the legs of female patients and more on the trunk of male patients (P < 0.001).
Conclusions: There is a divergence between the rapidly increasing incidence and the slower increase in mortality of CMM. This cannot be explained by a removal of the melanoma at a thinner thickness. Differences between the sexes according to the tumor site and the increasing rate of CMM containing benign naevus cells could implicate changes in the tumor biology. Public education in Sweden concerning ultraviolet radiation and the connection with melanoma is fairly new and might not have any influence on this time period. Additional investigation is needed to clarify this matter.