Breast cancer risk in women with neurofibromatosis type 1: a register-based cohort study from Denmark and Sweden.

An increased risk of breast cancer has been reported in women with neurofibromatosis type 1 (NF1), especially at younger ages, and NF1-related breast cancer has been associated with poor survival. We performed a large population-based cohort study to estimate the age-related breast cancer risk and survival in Danish and Swedish women with NF1. We used national registers to identify all women with a diagnosis of NF1 in Denmark and Sweden born between 1930 and 1990 (Denmark) or 1987 (Sweden). Age- and sex-matched comparisons were randomly selected from population registers. Cox proportional hazards models were used to study the association between NF1, breast cancer risk, and overall 5-year mortality after a breast cancer diagnosis. We included 2164 women with NF1 and 71 586 comparisons. A two-fold increased risk of breast cancer was observed in women with NF1 (hazard ratio (HR) 1.94, 95% confidence interval (CI) 1.59-2.36). The strongest association was observed in women between 30 and 39 years of age (HR = 3.98, 95% CI 2.16-7.32). Five-year mortality after a breast cancer diagnosis was higher in women with NF1 (HR = 1.98, 95% CI 1.31-2.99). Our results suggest that although increased, the risk of breast cancer in women with NF1 is not as high as previously reported, particularly among young women. These findings add to previous data and will contribute to the gathered knowledge needed to accurately address the risk of breast cancer in women with NF1.