Toxicity and Cosmetic Outcome of Breast Irradiation in Women with Breast Cancer and Autoimmune Connective Tissue Disease: The Role of Fraction and Field Size.

Purpose: Hypofractionation has historically been underused among breast cancer patients with connective tissue diseases given a theoretical risk of increased toxicity and their overall underrepresentation in clinical trials that established hypofractionation as standard of care. We aim to compare the rates of toxicity in patients with autoimmune connective tissue diseases treated with conventionally fractioned radiation therapy (CF-RT) and hypofractionated radiation therapy (HF-RT) including accelerated partial breast irradiation.

Methods: A total of 1983 patients treated with breast conservation between 2012 and 2016 were reviewed for diagnosis of autoimmune disease. Univariate analysis using binary logistic regression was performed to evaluate the effect of disease and treatment variables on acute and late toxicity. Multivariate analyses using Cox regression models were used to evaluate the independent associations between covariates and the primary end points. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated for reach risk group.

Results: Ninety-two patients with autoimmune disease were identified. Median follow-up was 59 months. Of the patients 35% received CF-RT and 65% received HF-RT, of whom 70% received whole breast radiation (WBI) without regional nodal irradiation, 12% received WBI with regional nodal irradiation, and 18% received accelerated partial breast radiation. Patients who received CF-RT were significantly more likely to have autoimmune disease (AD) symptoms (78% vs 37%, P <.001), to be managed on disease-modifying antirheumatic drugs (DMARDs; 41% vs 15%, P = .013), and to have active autoimmune disease (84% vs 43%, P <.001). On multivariate analysis, HF-RT was associated with a significantly decreased odds of acute and late grade 2/3 toxicity compared with CF-RT fractionation (acute: OR 0.200, 95% CI 0.064-0.622, P = .005; late: OR 0.127, 95% CI 0.031-0.546, P = .005).

Conclusions: Hypofractionation including accelerated partial-breast irradiation is associated with less acute or late grade 2/3 toxicity in this population.