1. Development of subsequent primary invasive melanoma following a first invasive or in situ lesion was significantly increased when compared to the age- and sex-matched general population.
2. Relative risk of subsequent primary invasive melanoma (SPIM) was greatest at the body site of the original invasive lesion, particularly the head.
Evidence Rating Level: 2 (Good)
Study Rundown: The increased risk of SPIM has been correlated to both previous diagnosis of initial primary in situ melanoma and to body region of initial invasive melanoma. However, relative risks by body site have not been previously identified. Therefore, these authors examined whether body region, sex, age group, and time since diagnosis influenced the likelihood of a SPIM. The body site of first primary invasive melanoma had no significance on overall relative risk of SPIM, but an initial in situ melanoma on all body regions except the head correlated with higher relative risk of developing SPIM. The body site with the greatest risk of SPIM was the region of the original invasive lesion for all subgroups. Additionally, females with a first primary invasive melanoma on the head were more likely to acquire a SPIM compared to males, and the highest risk of developing SPIM in both sexes was within the first year of initial diagnosis. Strengths of this study include its large population size and participant diversity within the Queensland area. However, the replacement of a control population by standardized incident ratio calculations may be considered a weakness.
In-Depth [retrospective cohort]: This study reviewed 39,668 eligible cases of first primary invasive melanoma and 22,845 cases of first primary in situ melanoma between 1982 and 2005 in Queensland, Australia. Among those, a total of 5,358 patients were diagnosed with SPIM and included in the study cohort. Standardized incidence ratios (SIRs) were used to measure relative risk and the significance of differences between SIRs was calculated using negative binomial regression. Results indicated that development of SPIM was 5.4 times more likely (SIR, 5.42; 95% CI, 5.23-5.61) in people with first primary invasive melanoma and 4.6 times more likely (SIR, 4.59; 95% CI, 4.37-4.82) for those with a first in situ primary melanoma than the general population. For all subgroups, SPIM development was most significant at the site of the original invasive or in situ melanoma, particularly for females with first primary invasive melanoma on the head (SIR, 13.32; 95% CI, 10.28-16.98). Overall, though, the body region of the first primary invasive melanoma had no effect on the relative risk of SPIM development in the study cohort (P =0.27).
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