SAN FRANCISCO Acral lentiginous is the rarest of the major histologic subtypes of melanoma, but is the most common subtype in blacks, according to a national study.
The study showed that the age-adjusted incidence of acral lentiginous melanoma (ALM) is similar in black and non-Hispanic white patients at about 1.8 cases per 1 million person-years. But ALM accounted for close to 40% of all cutaneous melanomas in blacks, whereas two-thirds of melanomas in non-Hispanic whites were of the superficial spreading subtype and ALM accounted for less than 2%, Dr. Porcia Bradford reported at the annual meeting of the American Academy of Dermatology.
Her analysis of the National Cancer Institute's Surveillance, Epidemiology, and End Results (SEER) database for 1986-2005 turned up 1,413 cases of histologically-confirmed ALM in 16 participating cancer registries. This was the first population-based study focusing on ALM, according to Dr. Bradford of the division of cancer and epidemiology, National Cancer Institute, Bethesda, Md.
The incidence of ALM was greatest in Hispanic whites, at 2.5 cases per 1 million person-years. The rate was lowest in Asian/Pacific Islanders at 1.1 cases per 1 million person-years. ALM comprised about 20% of all melanomas in Asian/Pacific Islanders and 10% of those in Hispanic whites.
The prognosis for individuals with ALM was significantly worse than for cutaneous melanoma as a whole. Five- and 10-year melanoma-specific survival rates for cutaneous melanomas overall were 91% and 87%, respectively, compared with 80% and 68% for ALM.
This disparity in outcomes was related in part to the fact that ALMs tended to be thicker at diagnosis. For example, 70% of all cutaneous melanomas were 1 mm thick or less, and 10-year melanoma-specific survival for patients with such tumors was 95%, whereas only 41% of all ALMs were 1 mm thick or less, and their associated 10-year survival was 88%. Mortality in Asian/Pacific Islanders and Hispanic whites was worse than in blacks or non-Hispanic whites with ALM. This appeared to be a result of the greater tumor thickness and more advanced stage at presentation of ALM in Asian/Pacific Islanders and Hispanics; after controlling for these variables, there were no longer significant racial differences in 5- and 10-year melanoma-specific survival for ALM.
The analysis demonstrated that the incidence of ALM has remained steady during the last couple of decades, while rates of other forms of melanoma have increased steadily.
Acral lentiginous melanoma accounted for almost 40% of all cutaneous melanomas in black patients and 2% in non-Hispanic white patients. Photos courtesy Dr. Gary Peck/Dr. Cherie Young