Short-term preoperative endocrine therapy allows to estimate and revert patient prognosis with further treatment plan correction in HR+ HER2- early breast cancer patients.

Abstract

e12628 Background: The anomaly function of ER/PR-dependent molecular cascade is a key driver of ER-positive HER2-negative breast cancer (HR+ HER2- BC) progression. Ki67>10% and/or grade 3 (G3) determine the initial poor patient (pts) prognosis in this group. The short-term pre-operative endocrine therapy (P-ET) simply allows to look ahead to properly the further adjuvant therapy (AT) and to estimate the endocrine therapy (ET) sensibility of each pts in the routine clinical practice. The existing diagnostic methods weaknesses for the baseline lymph nodes invasion, high BC heterogeneity do not allow to accurately estimate the disease stage and tumor phenotype, respectively, with 100% accuracy before surgery. In addition to pre-ET the post-operative IHC is a base method for further pts treatment plan especially for high heterogenicity breast tumors. Our study is focused on pts proportion estimation with P-ET benefit or tumor phenotype reversion in patients with early HR+ HER2- BC. Methods: HR+ HER2- BC pts stages I-II any level of Ki67 independent from grade have received P-ET (letrozole (L)/anastrozole (A)/tamoxifen (TAM)) no less than 2 weeks until surgery in MCSC named after A.S. Loginov. Enrollment period runs from Jun’21 and will end with 1,000 pts. The primary goal of the study was pts’s proportion evaluation with baseline Ki67>10% who experienced suppression of the proliferation marker to 10% or less and/or phenotype change during P-ET followed by AT strategy amendment. Results: At the data cut-off (Jan’22) 832 pts (5 pts were men) with HR+ HER2- BC were enrolled (IIT population) with median age 61 (range:26-85) and ECOG 0-2. 736 (89%) pts have baseline Ki67>10% of whom 100 (14%) pts - with G3, 291 (35%) pts - with baseline Ki67≥30%. Tumors of the 398 (54%) pts suppressed proliferation marker Ki67≤ 10% and 352 (88%) pts among them avoid planned adjuvant chemotherapy followed by ET prolongation independent of ET type (L/A/TAM). The median time of P-ET amounted to 39,5 days (range: 14-90) in focused group. Post-operative evaluation of specimens in 20 (2,4%) pts have resulted in the identification of phenotype change to HER2+ BC and TNBC with subsequent modification of AT decisions (including anti-HER2-based and/or dose dense regimens). Conclusions: In HR+ HER2- early BC pts short-term P-ET simply allows to estimate pts prognosis and further AT strategy proper planning: to identify the pts population of whom CT can be avoided while maintaining treatment efficacy with a better quality of life (42% pts of IIT) (1), to radically change the planned AT to achieve optimal treatment results (2,4% pts of IIT) (2).