Hormone receptor-positive, HER2-negative, pT1ab N0 breast cancers (BC) are generally estimated as having a low risk of recurrence after locoregional treatment and adjuvant treatment decisions could be challenging. We examined the impact of endocrine therapy (ET) +/- chemotherapy on outcomes in this population.
A total of 4,788 patients with pT1ab N0 HR+ HER2- BC were identified from a large cohort of 22,475 consecutive patients who underwent primary surgery at 15 French centres between 2000 and 2014. Endpoints were disease-free survival (DFS) and overall survival (OS). Analyses of causal effect using propensity scores were realized using a logistic regression including age, tumour size, histology, grade, and lymphovascular invasion (LVI).
Of 4,779 patients with pT1ab HR+ HER2- BC, 846 patients did not receive any adjuvant treatment and 3,933 received ET, among which 251 received chemotherapy. Age ≥ 70y, ductal histology, high grade and tumour size > 5mm were independently associated with ET prescription. Age ≤ 40y, LVI and high grade, were independently associated with chemotherapy prescription. At a median follow-up of 47.7 months, ET was independently associated with a significant DFS benefit in multivariate analysis (HR: 0.60 [0.41-0.89]; p = 0.011) with 5-year estimate DFS of 94% (CI95 [92-96%]) without ET vs. 96% (CI95 [95-97%]) with ET, while addition of adjuvant chemotherapy was not (HR: 0.90 [0.39-2.09]; p = 0.813). These results were supported by the analyses of causal effect using propensity scores (HR: 0.48 [0.28-0.83]; p = 0.009 for ET, and HR: 1.54 [0.11-21.8]; p = 0.78 for chemotherapy). OS was not significantly impacted by systemic treatments despite a trend for ET in multivariate (HR: 0.60 [0.36-1.00]; p = 0.051) and in propensity score analyses (HR: 0.52 [0.24-1.11]; p = 0.092).
Adjuvant endocrine therapy is associated with a survival benefit in pT1ab N0 HR+ HER2- BC even with a relatively short follow up. Consistent with current consensus guidelines that do not recommend adjuvant chemotherapy in these tumours, we did not find any benefit of adding chemotherapy to ET. These data provide additional clues to the issue of adjuvant systemic treatments in these tumours.
Has not received any funding.
All authors have declared no conflicts of interest.