Abstract PS1-12-14: Tolerance and clinical outcomes in elderly patients with hormone receptor positive breast cancer receiving CDK 4/6 inhibitors at a rural comprehensive cancer center

Abstract Background Cyclin dependent kinase 4/6 inhibitors (CDK 4/6is) are approved by the FDA in patients with HR+ metastatic and locally advanced breast cancer. Studies have shown that elderly women have similar clinical effects with CDK 4/6i use compared to younger women, but they experience higher rates of dose reductions and delays. The objective of this study was to evaluate real-world outcomes of elderly patients treated with CDK 4/6is to help elucidate the unique considerations necessary for treatment in the geriatric population. Our cancer center primarily serves rural and socioeconomically diverse patients who often require significant distance to travel for care. To evaluate the impact of potential geographic and socioeconomic disadvantages on the tolerance to CDK 4/6is and the clinical outcomes, we are investigating the impact of national and state area deprivation index (ADI) in this study, as we postulate that higher ADI may correlate with poorer clinical outcomes and tolerance. Methods This retrospective chart review was approved by the Institutional Review Board. Data gathering and analysis was performed by the authors. A total of 64 patients with HR+ breast cancer treated with ET and CDK 4/6i therapy aged 65 and over at the time of diagnosis who received care at the Dartmouth Cancer Center over the last five years were included in this study. Tolerance was defined by an aggregate score that incorporated the number of side effects, number of dose interruptions, number of dose reductions, and hospitalizations. National and state ADI were calculated by the regional zip codes. Results The median age at diagnosis was 72 years. 25% (16) patients had locally advanced disease and 75% (48) had metastatic disease at time of treatment. In patients with metastatic disease, median progression-free survival (PFS) was 10.5 months and median overall survival (OS) was 16.5 months. Median number of CDK 4/6i dose interruptions and reductions were 1 and 0, respectively. Median duration of dose interruption was 2 weeks. Median state and national ADI scores were 6 and 47, respectively. Neither state nor national ADI scores were significantly associated with tolerance. BMI was not significantly associated with tolerance. COX proportional hazard models did not show significant difference in survival outcomes in patients based on ADI (state ADI 5 or 5), age (less than 70 years vs. greater than 70 years), CDK 4/6i drug (abemaciclib vs. ribociclib vs. palbociclib), or endocrine therapy (anastrozole vs. fulvestrant vs. letrozole). Patients with higher ADI had a 1.4% higher hazard of death compared to those with lower ADI, but the p value is not significant (HR = 0.986). Older patients had a 15.5% lower hazard of death compared to younger patients, but the p value is not significant (HR = 0.845). Discussion/Conclusion Age, ADI, and BMI did not influence tolerance or outcome measures in our patient population. Pooled data from pivotal trials showed median PFS for patients over age 70 on CDK 4/6is and ET was 33.1 months, compared to 27.3 months in younger patients. Our patients (age 65+) had much lower median PFS of 10.5 months. This may be due, in part, to less fit patients and the presence of underlying comorbid conditions compared to more selective populations in pivotal trials. It is also possible that rurality itself may affect outcome measures in a distinct way that is not captured through ADI. Citation Format: C. Lapp, M. Afzal, X. Xia, T. MacKenzie, H. Kuznia, S. Haghollahi. Tolerance and clinical outcomes in elderly patients with hormone receptor positive breast cancer receiving CDK 4/6 inhibitors at a rural comprehensive cancer center abstract. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS1-12-14.