Real world experience with cyclin dependent kinase inhibitors in metastatic breast cancer from India.

e13003 Background: Patients in thehormone receptor positive/ herceptin2- (HR+/HER2-) subset have better prognosis among all molecular sub types of breast cancer, however, most patients ultimately progress on treatment with traditional endocrine therapies. The present study was conducted to evaluate the real world experience with Cyclin dependent kinase (CDK) 4/6 inhibitors Palbociclib and Ribociclib by evaluating the efficacy and toxicity profile in HR+/HER2- metastatic breast cancer. Methods: Thisstudy was conducted on the HR+/HER2- metastatic breast cancer patients who received Palbociclib/ Ribociclib in the first line or recurrent setting between January 2021 and January 2023 along with endocrine therapy. Clinical and demographic information and survival data was retrieved from the Hospital medical records. Results: Among a total of143 patients, 93 and 50 patients had received Palbociclib and Ribociclib, respectively. The most common factors in both the groups were age group 45-64 years (65.7%), postmenopausal status (65.7%), ECOG Performance status 1 (46.2%) and denovo disease at presentation (58%). The overall response rate was 90.2%. Majority of the patients showed partial response (64.3%) followed by stable disease (20.3%) in either group. In the patients receiving Palbociclib, a better median progression free survival (PFS) was observed in patients with ECOG performance status (PS) 1 (27.3 months, p-value < 0.0001), denovo disease (17.5 months, p-value 0.0155), first line hormonal therapy (22.5 months, p-value < 0.0001) and no prior chemotherapy (20.3 months, p-value 0.0001). Similarly, in the patients receiving Ribociclib, a better median PFS was observed in patients with ECOG PS 1 (22.2 months, p-value < 0.0001), denovo disease (21.7 months, p-value 0.0042), first line hormonal therapy 22.5 months (p-value < 0.0001) and no prior chemotherapy (21.7 months, p-value < 0.0001). On multivariate analysis, the factors significantly associated with PFS were ECOG PS, line of hormone therapy and prior chemotherapy (p-values < 0.0001, < 0.0001 & 0.0269, respectively). Anaemia & transaminitis were the most common toxicities in both drug cohorts [Palbociclib (97.8% & 75.3%, respectively) & Ribociclib (96.5% & 82%, respectively). Overall, dose modification due to toxicity was not required in 67.8% patients. Conclusions: The present study shows the real world experience with the effectiveness and tolerability of CDK inhibitors in metastatic breast cancer in India. However, large scale multi-centric studies are required to evaluate the pan India experience with these inhibitors.