Reproductive factors and risk of papillary thyroid cancer in women

The authors conducted a population-based case-control study of 410 women re siding in three counties in western Washington State who were aged 18-64 ye ars when diagnosed with papillary thyroid cancer in 1988-1994 and 574 contr ols to assess the effects of pregnancy history and other aspects of reprodu ctive life on risk of this disease. Among women aged 45-64, the authors obs erved no associations with number of live births, age at first live birth, or age at last live birth. Risk was somewhat increased in women <45 years w ho had given birth within the previous 5 years; this association was most e vident among women who reported that cancer symptoms had led to diagnosis. Among women who had given birth within the last 5 years, risk was greatest among those with two or more births during that time period (relative risk (RR) = 4.2, 95% confidence interval (CI): 2.0, 8.9, relative to parous wome n whose last birth was >5 years before the reference date), Risk of thyroid cancer was also associated with lactation during the previous 5 years (e.g ., RR = 2.9, 95% CI: 1.5, 5,5, among parous women who had breastfed greater than or equal to 12 months, vs. 0-1 months, during that interval). Our res ults suggest that thyroid stimulation during both pregnancy and lactation m ay result in a transient increase in risk of papillary thyroid cancer.