TRENDS IN TUMOR CHARACTERISTICS AND SURVIVAL OF MALIGNANT-MELANOMA, 1960-84 - A POPULATION-BASED STUDY IN SWEDEN

In Sweden, improvement in survival rates of patients with cutaneous ma lignant melanoma has counteracted the increase in incidence to produce a moderate rise in mortality. Our aim was to determine the possible i mpact of drift in diagnostic criteria, earlier diagnosis and changing biological features of the tumours upon trends in survival. We studied a stratified sample of 528 patients diagnosed between 1960 and 1984 i n a strictly defined geographical region. No evidence of drift in diag nostic criteria was found. The proportion of patients with invasion le vel Clark II increased from 3.2% in 1960-64 to 22.5% in 1980-84, the p roportion of thin melanomas (less than or equal to 0.75 mm) increased from 9.4% to 31.5% and the tumour thickness decreased significantly be tween each 5 year period of diagnosis. These changes are most likely t he results of earlier diagnosis. However, changes in tumour characteri stics have occurred, since the proportion of superficially spreading m alignant melanoma increased from 35% in 1960-64 to 51% in 1980-84 and the proportion of acral lentiginous melanoma decreased from 11% to 2%. The proportion of nodular melanomas remained fairly constant. The pro portion of tumours with lymphocytic reaction did not change, whereas t hose with histological regression increased slightly. Proportional haz ards analyses showed a significantly lower survival in patients diagno sed in 1960-64 but no apparent trend after 1965. This finding remained after adjustment for all studied clinical and histopathological facto rs which point towards changes in unmeasured biological features of th e disease.