Abstract 95P
Background
Postoperative radiotherapy after breast-conserving surgery in node-negative breast cancer halves the risk of local recurrence, though the absolute benefit varies depending on baseline risk of recurrence. In some subgroups, the benefit of radiotherapy is limited and might potentially justify a de-escalation approach with omission of radiotherapy. This Swedish multi-center prospective cohort study was designed to assess whether radiotherapy could be safely omitted in women ≥ 65 years with low-risk, estrogen-receptor (ER)-positive T1N0 breast cancer treated with breast-conserving surgery and adjuvant endocrine therapy for 5 years.
Methods
Eligible patients were women ≥ 65 years with unifocal, non-lobular, grade 1 or 2, ER-positive, pT1N0 breast cancer treated with breast-conserving surgery. Patients were prescribed endocrine therapy for 5 years and followed up with mammography at least annually for 10 years. The primary endpoint was local recurrence. Secondary endpoints were contralateral breast cancer, recurrence-free survival, and overall survival.
Results
The final study cohort included 601 patients with a median age of 71 years (range: 65 to 90) and a median tumor size of 11 mm (range: 3 to 20 mm). Median follow-up time was 119 months (interquartile range: 103 to 121 months). The cumulative incidence of local recurrence was 1.5% (95% Confidence Interval (CI): 0.8 to 2.8%) and 5.5% (95% CI: 3.8 to 7.6%) at 5 and 10 years, respectively. The cumulative incidence of contralateral breast cancer was 1.7% (95% CI: 0.9 to 3.0%) at 5 years and 4.5% (95% CI: 3.0 to 6.6%) at 10 years. The cumulative incidence of regional recurrence at 10 years was 1.4% (95% CI: 0.7 to 2.7%). Distant recurrence occurred in 5 patients (0.8%) during follow-up. The overall survival rate at 10 years was 83.1% (95% CI: 80.8 to 85.4%). In total, 3 patients (0.5%) died due to breast cancer during follow-up.
Conclusions
Our long-term study results support the emerging evidence on the possibility to omit radiotherapy after breast-conserving surgery in a well-defined subgroup of women aged 65 years or more with low-risk ER-positive pT1N0 breast cancer receiving adjuvant endocrine therapy.
Legal entity responsible for the study
Region Örebro County.
Funding
The Local Research Committee, Örebro University Hospital, OLL-589691 and the Key Foundation, Örebro University Hospital, Örebro, Sweden.
Disclosure
A. Valachis: Financial Interests, Institutional, Research Grant, Research Grant for a research project on Molecular profiling of triple negative breast cancer: Roche; Financial Interests, Institutional, Invited Speaker, PRODAT trial: Novartis; Financial Interests, Institutional, Invited Speaker, CHECKMATE-401 trial: Bristol Myers Squibb; Financial Interests, Institutional, Invited Speaker, CHECKMATE-76K trial: Bristol Myers Squibb; Financial Interests, Institutional, Invited Speaker, TELEPIK trial: Novartis; Financial Interests, Institutional, Invited Speaker, DESTINY-Breast09 trial: AstraZeneca. All other authors have declared no conflicts of interest.