Clinical Characteristics, Demographics, and Outcomes in Hormone-Receptor (HR+) Positive Metastatic Breast Cancer (MBC) Patients Treated with Palbociclib.

e13027 Background: The PALOMA-1 and PALOMA-3 studies demonstrated a significant progression-free survival (PFS) advantage for palbociclib (P) with letrozole or fulvestrant compared to these therapies alone. As patients allowed to participate in clinical trials do not mirror our heterogeneous patient population, application of these results is limited. We sought to further evaluate response to therapy in our diverse patient population. Methods: A retrospective review identified 58 patients treated with P for HR+ MBC after its FDA approval between January 1st, 2015 and October 1st, 2016 at our center in East Harlem, NY. Records were reviewed and clinical characteristics for each patient were analyzed. Results: The median age was 62 (range 34-84); 22.4% were ≥ age 70. Our cohort was 25% African American, 62.5% Caucasian, and 12.5% Asian American. 70.7% of patients were on an aromatase inhibitor and 29.3% were on fulvestrant. 48.3% had received prior chemotherapy. Median follow up was 18.2 months (95% CI 14.7, 20.2 months). Median event-free survival (EFS) was 11.0 months (5.3, 16.9 months). A partial response or better on imaging (34.5%) was associated with better EFS (HR 0.44 (0.22, 0.91) p = 0.027). Toxicity rate was 87.9%; 44.8% were ≥ grade 3. While toxicity (including ≥ grade 3) was not associated with worse OS or EFS, development of anemia was associated with worse EFS. An increase in MCV of > 10fL (HR 0.18 (0.09, 0.36) p < 0.001) and utilization of G-CSF support for neutropenia (HR 0.20 (0.05, 0.89) p = 0.035) were associated with better EFS. While age ≥70 was associated with worse OS (HR 4.03 (1.16, 14.00) p = 0.028), no difference in EFS or toxicity was observed including when neutropenia and anemia were evaluated independently. There was no difference in OS or EFS based on race or ethnicity. Conclusions: Our data confirm significant improvement in EFS in a real-world patient population with no differences based on race, extreme age, or general development of toxicity. Improved EFS seen with G-CSF support and increase in MCV warrant further investigation. A review of pathologic correlates as potential biomarkers of response based on these clinical results is underway.