252P Impact of HER2 expression levels on survival in patients with hormone receptor positive and HER2 negative advanced breast cancer and treated with ribociclib and palbociclib in combination with endocrine therapy: A real-life data, Turkish Oncology Group study

There is limited data on the effect of CDK 4/6 inhibitors in patients with advanced HR-positive and HER2-low tumors. Here we report real-life retrospectively collected from 448 ER-positive/HER2-negative breast cancer treated ribociclib palbociclib (only both them reimbursed) plus endocrine therapy June 2016 to 2022. The outcome HER2-0 (IHC score) (HER2 IHC score1+ 2+) tumors were compared. 443 female (98.9%). Median age was 58 (25-90). While HER2 score 0 295 (65.8%), 1-2 (HER2-low) 153 (34.2%). OS could not be calculated at follow-up, an estimated 71% alive 36 months. median PFS 29.4 months (95 CI, 16.3-42.6). mPFS HER2-negative patient group 27.7 (95% 11.2-44.2) there no significant difference for receiving or this subgroup (p=0.11). 117 1 positive patients, 22 had disease progression. NE (at 12 months, 82% 24 57% progression free). 2 6 72% No found between population HER2-negative, 1+ 2+ ISH negative terms (p=0.163). In addition, when evaluated separately subgroups, those (p=0.50 p=0.70, respectively). Although number decreased subdivided our study, showed that expression did show a statistically impact survival metastatic first-line setting.