Risk of breast cancer in women with non-lactational mastitis.

Little is known regarding the association of non-lactational mastitis women with breast cancer risk. This population-based cohort study examined the breast cancer risk in women with non-lactational mastitis. We identified 3,091 women with non-lactational mastitis between 2000 and 2011 using the Taiwan National Health Insurance Research Database. We performed 1:4 propensity score matching by age, socioeconomic status and comorbidities and identified 12,364 women without non-lactational mastitis. The mean age of women with non-lactational mastitis was 37.9 years; these women had a higher breast cancer risk than the comparison group (adjusted hazard ratio = 1.94, 95% confidence interval: 1.30-2.90). The incidence rates of breast cancer in women with non-lactational mastitis and the comparison group were 14.79 and 7.57 per 10,000 person-years, respectively. Furthermore, non-lactational mastitis was a risk factor for breast cancer in women aged <50 years, women with lower socioeconomic status and women with hormonal medication (p < 0.05). Women who had more episodes of non-lactational mastitis had a higher risk of developing a breast cancer. Thus, the risk of breast cancer in women with non-lactational mastitis is significantly higher than those without non-lactational mastitis.