Abstract P5-11-18: Real-world evidence of efficacy and activity of palbociclib plus endocrine therapy and post-progression treatments in HR+/HER2- metastatic breast cancer patients: The PALPract study

Background: Several randomized clinical trials clearly demonstrated that adding palbociclib (P) to endocrine therapies (ET), such as letrozole (LT) or fulvestrant (FLV), significantly improves outcome both in first-line/endocrine sensitive and second-line/endocrine resistant hormone receptor positive (HR+), human epidermal growth factor receptor 2 negative (HER2) metastatic breast cancer (MBC) patients (pts). The aims of the present study were to assess efficacy, activity and toxicity of P combined with either LT or FLV in a real world setting, and to study the efficacy and activity of treatments administered after progression to P + ET. Methods: Records of 245 consecutive HR+/HER2- MBC patients from 14 Italian cancer centers were reviewed in this observational study. Primary end-point was progression-free survival (PFS) obtained with P+ET; secondary end-points were overall response rates (ORR) and clinical benefit rate (CBR) obtained with P+ET and with post-progression treatments, as well as overall survival (OS), PFS to subsequent treatment lines and post-progression survival (PPS). Results: Overall 245 pts were treated with P+ET from April 2014. Of them, 116 (47%) received it in first-line setting, 70 (28%) in second-line and the rest (68 pts, 25%) in subsequent lines. Median age was 60 (35-80) years and median ECOG performance status was 0. Seventy-three pts (30%) had more than two metastatic sites and 75 (31%) had visceral metastasis. Ninenty-one (37%) pts received P+LT and 92 (37%) were treated with P+FLV. For 15 (6%) premenopausal pts an LHRH analogue was added to P+ET. In 77 (41%) patients a biopsy of a metastatic lesion was performed. Among the 116 pts treated in first-line setting, median PFS was 14.7 (95% CI 12.0-17.3) and 15.1 (95%CI 8.6-21.6) months for pts receiving P+LT and P+FLV, respectively. ORR was 48% (95% CI: 39-57%) and CBR was 75% (95% CI, 66-82%). Four (3%) complete responses (CR), 52 (45%) partial responses (PR), 31 (27%) stable disease (SD) and 11 (9%) progression disease (PD) were observed as best response; 18 pts were not yet evaluable. Among the 70 pts treated in second-line setting, median PFS was 10.8 (95%CI 0-24.3) and 7.9 (95%CI 3.3-12.5) months, for pts receiving P+LT and P+FLV, respectively. The ORR was 26% (95% CI: 16-38) and the CBR was 66% (95% CI, 53-76). One CR (1%), 17 PR (24%), 28 SD (40%) and 13 PD (18.5%) were observed as best response, while 9 were not yet evaluable. Best response was achieved after a median of 5 cycle. At time of the current analysis, 50 pts experienced PD during P+ET. Of them, 38 (76%) received chemotherapy (capecitabine, eribulin, nab-paclitaxel, paclitaxel+bevacizumab, vinoreline) and 12 (24%) ET. To date, only 5 pts progressed during these therapies, preventing us for evaluating secondary end-points regarding efficacy and activity. The most frequent adverse event (AE) was grade 3-4 neutropenia (31%), with febrile neutropenia reported in 5 (2%) cases. Main non-hematological AEs were fatigue and gastrointestinal symptoms (diarrhea and stypsis). Conclusions: Our findings confirm the efficacy and safety of P+ET as first/second-line treatment for HR+/HER2- MBC pts, even in a non-selected, real world population. Since data regarding the efficacy and activity of post-progression therapies were not mature at the time of the current analysis, they will be subsequently presented. Citation Format: Alessandra Fabi, Michelangelo Russillo, Mariangela Ciccarese, Simone Scagnoli, Francesco Schettini, Giuseppe Buono, Vito Lo Russo, Grazia Arpino, Rosalba Rossella, Giuseppina Sarobba, Marianna Giampaglia, Patrizia Pellegrini, Simonetta Stani, Michela Palleschi, Vincenzo Adamo, Francesca Morelli, Maria Agnese Fabbri, Cecilia Nistico, Gianluigi Ferretti, Giovanna Catania, Simona Pisegna, Diana Giannarelli, Francesco Cognetti. Real-world evidence of efficacy and activity of palbociclib plus endocrine therapy and post-progression treatments in HR+/HER2- metastatic breast cancer patients: The PALPract study [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P5-11-18.