Pigmentary traits, family history of melanoma and the risk of endometriosis: a cohort study of US women.

BACKGROUND Endometriosis has been associated with a higher risk of cutaneous melanoma, but the mechanisms underlying this association are unknown.Some constitutional factors known to influence melanoma risk have been associated with endometriosis in some retrospective studies. However, prospective data are scarce, and more research is needed to confirm this potentially novel endometriosis risk profile. METHODS To investigate the relationships between pigmentary traits, family history of melanoma and endometriosis risk, we analysed data from the Nurses’ Health Study II, a cohort of 116 430 female US nurses aged 25–42 years at inclusion in 1989. Data were collected every 2 years with 20 years of follow-up for these analyses. We used Cox proportional hazards regression models to compute relative risks(RRs) and 95% confidence intervals (CIs). RESULTS During 1 212 499 woman-years of follow-up, 4763 cases of laparoscopically-confirmed endometriosis were reported among premenopausal Caucasian women. Endometriosis risk was increased with presence of naevi on the lower legs (RR=1.08, 95% CI=1.021.14) and higher level of skin’s burning reaction to sun exposure in childhood/adolescence (‘burn with blisters’: RR=1.20,95% CI=1.061.36) compared with ‘practically none’;P(trend)=0.0006) and family history of melanoma (RR=1.13, 95%CI=1.011.26). CONCLUSION This assessment reports modest associations between several pigmentary traits, family history of melanoma and endometriosis risk,corroborating the results from previous retrospective studies. Our findings call for further research to better understand the mechanisms under lying these associations.