Background: The benefit of radiotherapy in older women with endocrine responsive early breast cancer treated with breast-conserving surgery and endocrine therapy is unclear. The aim of this study was to verify if omission of radiotherapy in a predefined cohort of patients with good prognosis early breast cancer after breast conservation is safe.

Methods: Eligibility criteria were: consecutive patients with age ≥ 65 years, breast-conserving surgery (sector resection + sentinel node biopsy), clear margins, unifocal T 1 N0, Elston grade 1 and 2, estrogen receptor-positive. After informed consent adjuvant endocrine therapy, either tamoxifen or an aromatase inhibitor, was prescribed for 5 years. Primary endpoint was ipsilateral breast tumor recurrence (IBTR). Secondary endpoints were contralateral breast cancer, recurrence-free survival (RFS) and overall survival (OS).

Results: Between 2006 and 2012, we included 603 women from 14 Swedish centers. Two patients did not fulfill the inclusion criteria and were excluded from the analysis. Median age was 71 years (range 65 to 90). At a median follow-up of 59 months (range 2 to 110) 13 IBTR (cumulative incidence at five years, 1.3% (95% CI, 0.6% to 2.7%), 4 regional recurrences (one combined with IBTR), 2 distant recurrences both without IBTR or regional recurrence and 11 contralateral breast cancers was observed. Twenty-nine patients were diagnosed with tumors of other origin. Seven of them were endometrial cancers. There were 39 deaths. Only one of the deaths (2.6%) was due to breast cancer and 11 (28.2%) were due to other cancers (2 endometrial cancers). Five-year overall survival was 93.9% (95% CI, 91.4% to 95.7%).

Conclusion: This study demonstrates, with a median follow-up of 59 months, that breast-conserving surgery and endocrine therapy without radiotherapy is a safe treatment option in women with early breast cancer and favorable histopathology aged ≥ 65 years. The risk of IBTR is comparable to the risk of contralateral breast cancer. The low rate of breast cancer deaths indicates that breast cancer mortality is of secondary importance in this subset of women.

Citation Format: Villman KKA, Wickberg Å, Killander F, Lindman H, Bjöhle J, Edlund P, Tennvall-Nittby L, Bachmeier K, Carlberg M, Blomqvist C, Ahlgren J, Liljegren G. Omitting radiotherapy in women ≥ 65 years with early breast cancer and favorable histopathology after breast-conserving surgery, sentinel node biopsy and adjuvant endocrine therapy is safe [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P1-10-05.