Comparison of the effectiveness of intraoperative radiotherapy with external beam radiotherapy in patients with early breast cancer

Background. Breast cancer is the most common cancer in women. The main treatment for breast cancer includes surgery, chemotherapy, radiation therapy, and hormone therapy. The role of radiation therapy in the management of breast cancer continues to evolve. Radiation therapy is currently being de-escalated to include the use of intraoperative radiotherapy (IORT) and adjuvant endocrine therapy. Purpose of the study: to compare the efficacy of IORT with that of external beam radiotherapy (EBRT) in the treatment of early breast cancer. Material and Methods. A retrospective study of 559 patients with early breast cancer was conducted in Clinical Oncology Center of Saint Petersburg. The main treatment group included 273 patients who underwent breast-conserving surgery with IORT and sentinel lymph node biopsy. The control group included 286 patients who underwent breast-conserving surgery with sentinel lymph node biopsy and EBRT. Results. For all patients, the median follow-up time was 59.1 months (interquartile range: 43.7 to 80.7), the minimum follow-up period was 0.6 months, and the maximum follow-up period was 110.4 months. Recurrence occurred in 18 (6.6 %) patients of the main group and in 8 (2.8 %) patients of the control group. A statistically significant association of biological subtype with survival outcomes was found (p=0.02). The hazard ratio for Luminal B of 1.88 (95 % CI 1.02, 3.46) corresponded to a 65 % chance of an earlier onset of a negative outcome. The hazard ratio for triple-negative breast cancer of 3.01 (95 % CI 1.53, 5.95) corresponded to a 75 % chance of an earlier negative outcome. In the main treatment group, 11 (4 %) patients developed disease progression, and 2 of them died of multiple organ failure. In the control group, disease progression was observed in 18 (6.3 %) patients, 6 of whom died. However, the analysis of overall survival using the Kaplan–Meier curve showed a statistically non-significant log-rank p-value (0.73). The 3-year survival rates were 100 % (100 – 100) in the treatment group and 98.2 % (96.7 – 99.8) in the control group. The 5-yaer survival rates were 99.3 % (97.9 – 100) in the treatment group and 97.8 % (96.2 – 99.6) in the control group. These results showed advantage of IORT over EBRT. Conclusions. Intraoperative radiotherapy is a safe and effective alternative to external beam radiotherapy for early breast cancer.

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