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

Abstract

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