Abstract PS10-55: Palbociclib real-world data in metastatic breast cancer: A multi-site report of survival and adverse events in routine clinical practice in Scotland
Authors: Oswald Ailsa J , Hall Peter , Turnbull Arran , Oikonomidou Olga 
Published: February 2021

Background: Palbociclib, with endocrine therapy, has demonstrated clinical benefit in patients with ER+ve HER2-ve metastatic breast cancer in randomised controlled clinical trials. Further observational data is beneficial to illustrate how these results translate into benefit in routine practice. Furthermore, detecting predictors of response aids clinical decision-making. Our primary aim was to report the survival data and adverse event (AE) rates in a real-life population treated with palbociclib. Secondarily, we aimed to identify predictors of response. Method: We retrospectively analysed 150 patients with metastatic breast cancer treated with palbociclib and endocrine therapy in routine clinical practice, over 3 years in three sites across South East Scotland. Baseline demographics (including disease site, prior treatment, bloods), progression data, AE rates, delays/dose reduction (DR) were recorded. For statistical analysis, we calculated actuarial rates of progression and breast cancer specific survival (BCSS) for the whole cohort. Survival analysis was performed using Kaplan-Meier and cox regression statistics. Statistical associations between variables were analysed by generalised linear models with chi-square statistics. Results: The average patient age was 61.4 years and most were post-menopausal (86.7%). Around two thirds (63.3%) were previously treated adjuvantly and most were performance status 0 (51.3%) or 1 (44.0%). Commonest disease sites were bone (76.0%), liver (46.0%), lung (42.7%) or nodes (36.7%). Patients were prescribed palbociclib with either; aromatase inhibitor (AI) (74.0%) as 1st line or fulvestrant (26.0%) as 2nd line. Standard starting dose was 125mg (87.3%). Rationale for a lower starting dose was mainly due to patient age (78.9%), by physician’s choice.For the whole cohort, the actuarial progression rate at 24 months was 0.45 (95%CI±0.12) and BCSS rate was 0.69 at 24 months (95%CI±0.16). In the AI sub-group (n=111), at 12 months, the actuarial progression rate was 0.26 (95%CI±0.10) and BCSS rate was 0.86 at 12 months (95%CI±0.08). In the fulvestrant sub-group (n=39), the actuarial progression rate was 0.56 (95%CI±0.25) and BCSS was 0.82 (95%CI±0.14) at 12 months. Most common sites of progression were; visceral (84.1%), bone (40.1%), nodal (18.2%) or chest wall (6.8%). less had progressive disease (11.7% vs. 42.8%), compared to the fulvestrant group (n=28). The commonest AE was fatigue. During treatment, 67.1% had grade 3/4 neutropenia. Neutropenic sepsis rates were low (1.3%). Around half (47.9%) required DR, mainly for neutropenia (81.4%). A lower baseline ANC was associated with a lower ANC during cycle 1 (p&lt;0.001) and increased likelihood of DR (p=0.001). Age, disease site and prior chemotherapy did not predict neutropenia. On multivariate analysis for predictors of response, patients were more likely to progress if they had liver involvement (OR 3.5, 95%CI 1.6-7.4, p=0.001) or had previous endocrine therapy in the adjuvant setting (OR 1.74, 95%CI 1.1-2.8, p=0.019). Those who had a DR were significantly less likely to progress (OR 0.23, 95%CI 0.9-0.6, p=0.001). Discussion: Our real-world clinical data of the use of palbociclib illustrates it is an effective therapy in a heterogeneous population, with a progression rate of 45% at 24 months. Neutropenia was common but neutropenic sepsis rates were very low, similarly to the pooled PALOMA safety data. The only predictor of neutropenia was baseline ANC. Those who had prior endocrine therapy or with liver involvement were more likely to progress. Interestingly, those with a DR were significantly less likely to progress. Other observational data has produced mixed results with regard to this relationship and therefore larger studies are needed to validate these findings.

Citation Format: Ailsa J Oswald, Peter Hall, Arran Turnbull, Olga Oikonomidou. Palbociclib real-world data in metastatic breast cancer: A multi-site report of survival and adverse events in routine clinical practice in Scotland [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS10-55.