Malignant melanoma in southern Arizona. Increasing incidence and sunlight as an etiologic factor.

This study demonstrated an increasing incidence of malignant melanoma during the past ten years and a very high incidence of this tumor in southern Arizona. During the ten-year period, 533 melanomas were removed from white patients. Of these, 52% were male and 48% were female. The number of melanomas increased yearly, from 20 in 1969 to 120 in 1978, a crude rate incidence of 6.49 to 28.57 (27.20 standardized) per 100,000, respectively. This reflects an average annual increase of 34% to 37% and a 340% increase for the period. The highest incidence of tumor was in the 50 to 59 year and 60 to 69 year age groups. The most common site of occurrence was the back, with twice as many tumors arising there in males. The legs were involved in 13% of patients, with an occurrence rate eight times higher in females. The extremely high incidence of melanomas in southern Arizona is probably due to meteorologic and geographic factors allowing large amounts of ultraviolet light to reach the earth's surface.