Is superficial spreading melanoma still the most common form of malignant melanoma?

Abstract

Most epidemiological studies suggest that superficial spreading melanoma is the most common histological subtype of malignant melanoma, but past data may not reflect current patterns of sun exposure or other risk factors. We sought to determine the prevalence of melanoma subtypes among recent specimens in a South Texas dermatopathology practice. Lentigo maligna was the most common subtype of melanoma among the cases studied. Of 771 cases of melanoma reviewed, lentigo maligna and lentigo maligna melanoma accounted for 429 (56%). There were 220 cases of pagetoid (superficial spreading) melanoma (29%). Nodular melanoma with no apparent radial growth phase accounted for 27 cases (4%), and there were 23 cases of acral lentiginous melanoma (3%). The remaining 72 specimens (9%) included cutaneous metastases, spitzoid melanoma, melanoma in situ arising within a nevus, nevoid melanoma, desmoplastic melanoma, and patterns that could not be classified. Although the dermatopathology practice is located in South Texas, most patients are active duty military, military retirees, and military dependents. The majority currently resides in Texas, but the patients have lived in many locations around the world and traveled extensively. Sun exposure patterns and other risk factors may not reflect those of other populations. We were not able to perform subgroup analysis based on ethnicity or skin type as such data were not typically submitted with the specimens. Our results challenge the notion that pagetoid (superficial spreading) melanoma is the most common subtype of malignant melanoma, at least in patients with extensive sun exposure. Changing patterns of sun exposure or environmental factors may contribute to the changing epidemiology of malignant melanoma. The current prevalence of subtypes of melanoma should be studied in other populations.