Extended endocrine therapy after 5 years of adjuvant LHRH-agonist in premenopausal patients with node-positive hormone receptor (HR)-positive early breast cancer.

537 Background: There is no evidence regarding the benefit of extended endocrine therapy (eET) beyond 5 years of adjuvant treatment with LHRH agonists (LHRHa) in premenopausal women with node-positive, HR-positive early breast cancer (eBC). Methods: We conducted a retrospective study on two prospectively maintained datasets (Young Women Study and IEO Breast Cancer Dataset) to evaluate the clinical benefit of eET in women who had completed 5 years of adjuvant LHRHa, remained premenopausal, and had no evidence of distant or locoregional recurrence. This study included <40y women at diagnosis (between 2006 and 2016) with node-positive HR+ eBC, with ductal, lobular, or mixed histological subtypes, receiving or not eET (tamoxifen monotherapy or LHRHa+tamoxifen/aromatase inhibitor [AI]). The primary endpoint was the invasive breast cancer-free survival (IBCFS), calculated from the 5th year of endocrine therapy (ET) and adjusted for dataset, age at diagnosis, histotype, stage, disease subtype, type of adjuvant chemotherapy and ET received. Results: 503 patients were included (see Table): 287 received eET for a median duration of 3.6 years (Interquartile Range: 2.1–5.0). At a median follow-up of 7.05 years (calculated from the 5th year of ET), 50 and 72 IBCFS events occurred in the eET and non-eET groups, respectively. The adjusted Hazard Ratio (HR) for IBCFS comparing the eET to the non-eET group was 0.60 (95% CI,0.41-0.88; p<0.001). For distant recurrence or death, 28 and 46 events occurred, respectively, and the adjusted HR for distant disease free-survival was 0.43 (95% CI, 0.27-0.71). Among patients receiving eET, the adjusted HR for IBCFS comparing tamoxifen monotherapy (n=137) with LHRHa+tamoxifen/AI (n=150) was 0.75 (95% CI, 0.41-1.38). Conclusions: Extending endocrine therapy beyond five years of LHRHa treatment resulted in significantly higher IBCFS and distant metastasis free-survival. Larger prospective studies are required to confirm this finding and determine the most effective eET strategy. Patients' characteristics. Characteristic Extended endocrine therapy(N=287) No extended endocrine therapy(N=216) Age at diagnosis, median (IQR) 37 (35-39) 37 (33-39) Dataset: IEO | YWS, n 273 | 14 212 | 4 Histotype: ductal | lobular | mixed, % 91 | 5 | 4 95 | 3 | 2 pT: pT1 | pT2 | pT3-4, % 37 | 48 | 15 41 | 52 | 7 pN: pN1 | pN2 | pN3, % 64 | 22 | 14 73 | 17 | 10 Luminal A-like | B-like (G3 or HER2+), % 47 | 53 49 | 51 LHRHa combination during years 1-5: tamoxifen | aromatase inhibitor, % 66 | 34 76 | 22 Previous chemotherapy, % 77 70 Previous radiotherapy, % 64 62 G3, grade 3; IEO, European Institute of Oncology; IQR, interquartile range; YWS, Young Women Study.