Menstrual and reproductive factors in the risk of differentiated thyroid carcinoma in native women in French Polynesia: a population-based case-control study.

French Polynesia has one of the world's highest incidence rates of thyroid cancer. A case-control study among native residents of French Polynesia included 201 women diagnosed with differentiated thyroid cancer before the age of 56 years, between 1981 and 2004, matched to 324 population controls on date of birth. Face-to-face interviews were conducted from 2002 to 2004. Odds ratios were calculated by using conditional logistic regression and were reported in the total group and by ethnic group ("Polynesian" vs. "mixed"). The risk of thyroid cancer increased with natural (odds ratio = 1.9) or artificial (odds ratio = 4.5) menopause compared with that associated with a premenopausal status and with number of births (p for trend = 0.03): odds ratios for one, two, three, four or five, six or seven, and eight or more births were, respectively, 0.90, 1.6, 2.3, 2.2, 2.7, and 1.7 compared with a nulliparous status. Similar results were observed for Polynesian women. No association was observed with irregular menstrual cycles, age at menopause, history of miscarriage or induced abortion, time since last birth, age at and outcome of first pregnancy, or breastfeeding. This study confirms the role of menstrual and reproductive factors in the risk of differentiated thyroid cancer in Pacific island populations.