Smoking increases breast toxicity despite adjuvant hypofractionated IMRT in early breast cancer.

Objective: To evaluate the impact of smoking on acute and chronic toxicity in early breast cancer patients treated with hypofractionated intensity-modulated radiation therapy (IMRT) and a brachytherapy boost following breast-conserving surgery.

Methods: A retrospective study of 638 patients treated between 2009 and 2017, with 566 having recorded smoking status. Acute toxicity was assessed at treatment end and chronic toxicity at least one-year post-treatment, using Common Terminology Criteria for Adverse Events v4.0. Statistical analyses included chi-square tests and relative risk (RR) calculations.

Results: A total of 566 patients were included in the study, with 31.3% being smokers. The cohort was followed for a median of 6 years (range: 1-11 years). Acute toxicity was primarily characterized by radiodermatitis, with 87.6% of patients developing grade 1 and 5.5% experiencing grade 2. No cases of grade ≥ 3 were observed, and 6.9% of patients did not experience radiodermatitis. Bleeding was rare (1.1%) and infections occurred in 2.0% of patients. Regarding chronic toxicity, 67.1% of patients had no fibrosis, while 27.4% had grade 1 fibrosis. Grade 2 and grade 3 fibrosis were observed in 4.9% and 0.6% of patients, respectively, with no cases of grade 4 fibrosis. Edema was present in 8.0%, and 4.4% of patients reported chronic pain. When comparing smokers and nonsmokers, acute toxicity incidence, particularly radiodermatitis, was similar between the two groups. Smokers had a significantly higher incidence of chronic fibrosis (35.6% vs. 24.7%, p = 0.013) and chronic pain (7.9% vs. 3.3%, p = 0.024) compared to nonsmokers. However, there were no significant differences in the occurrence of edema between smokers and nonsmokers (7.9% vs. 8.0%, p = 0.879).

Conclusion: While advanced radiation techniques such as hypofractionated IMRT improve overall toxicity profiles, smoking significantly exacerbates chronic toxicity in breast cancer patients. This study underscores the urgent need for comprehensive smoking cessation programs as part of cancer care, addressing lifestyle factors to improve patient outcomes and quality of life.