Risk of radiotherapy-associated autoimmune bullous disease among Taiwanese patients with breast cancer: a case-control study

This study aimed to evaluate the association of autoimmune bullous diseases [bullous pemphigoid (BP) and pemphigus vulgaris (PV)] with radiotherapy (RT) among patients with breast cancer from a population-based Taiwanese database. The case-control study included 365 women with BP or PV and 1460 randomly selected propensity score-matched controls without BP or PV. We compared the prevalences of prior RT and breast cancer between the cases and controls. In addition, we performed multivariable logistic regression analysis to calculate the odds ratios (ORs) and 95% confidence intervals (CIs) for developing BP or PV according to previous RT and/or breast cancer status. Among the 1825 subjects, 680 patients (37.16%) had previously undergone RT, including 196 cases (53.41%) and 484 controls (33.08%) (P < 0.001). 288 of the 1825 subjects (15.78%) had breast cancer, including 90 cases (24.66%) and 198 controls (13.56%) (P < 0.001). The multivariable logistic regression analysis indicated that, after adjusting for comorbidities, urbanization level, level of care, and monthly income, elevated risks of developing BP or PV were associated with prior RT (adjusted OR: 1.744, 95% CI 1.343-2.511) and having breast cancer (adjusted OR: 1.574, 95% CI 1.025-1.889). An even greater risk of BP or PV was associated with the combination of previous RT plus having breast cancer (adjusted OR: 2.896, 95% CI 1.882-7.013). The present study's findings suggest that a significantly elevated risk of developing BP or PV is associated with previous RT and/or breast cancer.