MULTIPLE PRIMARY MELANOMAS - AN ANALYSIS OF CANCER REGISTRY DATA FROMVICTORIA AND NEW-SOUTH-WALES

All primary invasive cutaneous malignant melanomas (CMM) diagnosed in Victoria and New South Wales from 1985 to 1989 were obtained from the population-based cancer registries. Altogether 14,590 people with firs t CMMs were followed for at least 2 years, during which time 496 multi ple primary CMMs were identified. Of the study population, 3.4% develo ped a second primary CMM and 0.3% developed three or more. It was esti mated that 4.5% of people would develop a second CMM within 5 years of the first and that the risk was higher in males, particularly in men aged over 70 years. With regard to metachronous primaries, only age an d thickness of the first primary were significant predictors of the th ickness of the second: older people tended to have thicker CMMs and se cond CMMs were generally thinner than the first. Body site concordance was higher than expected by chance, particularly for synchronous diag noses. The high degree of site concordance of metachronous primaries l ent support to the hypothesis that skin adjacent to the first CMM migh t have undergone a 'field effect', rendering it at increased susceptib ility to malignancy.