Melanoma in Western Australia 1975-76 to 1980-81: trends in demographic and pathological characteristics.

Trends in incidence rates of cutaneous malignant melanoma in Western Australia from 1975-76 to 1980-1981 have been examined with reference to age, sex, body site, presence or absence of dermal invasion, tumour thickness, histological type, socioeconomic status and occupation. The incidence rates of all melanomas increased from 22.1 to 31.5 per 100,000 person-years in males and from 23.6 to 28.6 in females. In males, the relative annual increase in the incidence of invasive melanoma was 2.2%, and in females it was 5.6%. In-situ melanomas had larger relative increases in incidence (28% per annum in males and 10% in females) and the thickness of invasive lesions decreased between 1975-76 and 1980-81. The relative increase in incidence of invasive melanomas was greatest on the body sites with the highest rates initially--the trunk in males and the lower limbs in females. There was an increase in the proportion of invasive lesions classified as superficial spreading melanoma. The increase in incidence of in situ melanomas was largely restricted to the head and neck in older men of high socioeconomic status resident in Perth. This trend in in-situ melanoma was mainly due to an increase in the recorded incidence of Hutchinson's melanotic freckle. It may have been, in part, an artefact due to increased recognition of Hutchinson's melanotic freckle in this sub-group of the population.