359P - Overall survival of palbociclib (PAL) + endocrine therapy (ET) in Japanese patients with hormone receptor-positive (HR+)/ human epidermal growth factor receptor 2-negative (HER2-) advanced breast cancer (ABC) in the 1st line (1L) or 2nd line (2L) setting: A multicenter observational study

Background

Recently, we reported interim effectiveness results of PAL+ET for the treatment of HR+/HER2- ABC in Japanese routine clinical practice (Yoshinami et al., Breast Cancer, 2024), however, the number of survival events at the interim analysis was limited (32.6%). Here, we present results from the final analysis with 41.7% of events.

Methods

This multicenter, observational study, enrolled patients with HR+/HER2- ABC who initiated PAL+ET between 15 December 2017 to 31 December 2020 as 1L or 2L ABC treatment. Overall survival (OS), real-world progression-free survival (rwPFS), and chemotherapy-free survival (CFS) were estimated with the Kaplan-Meier method. Treatment-free interval (TFI) was defined as end date of adjuvant therapy to the diagnosis date of recurrence.

Results

The study enrolled 693 patients of which 426 (61%) and 267 (39%) received PAL+ET as 1L and 2L, respectively. Median age was 59.0 (range 29-87), 71.4%/67.7% of patients (1L/2L) were postmenopausal, 45.8%/39.3% had TFI <12 months, 20.4%/20.2% had TFI≥12 months, and 26.1%/28.1% had de novo metastatic disease at time of initial diagnosis. After 48.1 months median follow-up, median OS (95% CI) was 68.2 months (60.8-not reached) for 1L patients and 50.7 months (42.2-57.2) for 2L patients. Median rwPFS was 26.2 months (21.4-30.4) for 1L patients and 14.9 months (11.7-18.3) for 2L patients. Median CFS was 37.3 months (33.2-43.9) for 1L patients and 23.1 months (20.3-27.4) for 2L patients. 60.7%/61.1% of patients (1L/2L) received endocrine-based therapy as 1^st subsequent therapy following PAL+ET, including CDK4/6 inhibitors + ET for 23.1%/15.9% patients.

Conclusions

Our real-world study in Japanese routine clinical practice results are generally in line with those from other PAL studies. Median OS was >5 years with 1L PAL+ET, supporting the use of PAL+ET as 1 L for ABC in the real-world setting.

Clinical trial identification

NCT05399329.

Editorial acknowledgement

Legal entity responsible for the study

Pfizer Japan Inc.

Funding

Pfizer Japan Inc.

Disclosure

T. Nakayama: Financial Interests, Personal, Speaker, Consultant, Advisor: AstraZeneca, Daiichi Sankyo, Eisai, Novartis, Eli Lilly, Taiho, Chugai, Pfizer. S.E. Nagai: Financial Interests, Personal, Speaker, Consultant, Advisor: AstraZeneca, Daiichi Sankyo, Eisai, Eli Lilly, MSD, Taiho, Chugai, Pfizer. M. Hattori: Financial Interests, Personal, Speaker, Consultant, Advisor: Eli Lilly, Pfizer. T. Yoshinami: Financial Interests, Personal, Speaker, Consultant, Advisor: AstraZeneca, Chugai, Eisai, Eli Lilly, MSD, Pfizer. H. Masuda: Financial Interests, Personal, Speaker, Consultant, Advisor: Eli Lilly, Chugai, Pfizer. K. Watanabe: Financial Interests, Personal, Speaker, Consultant, Advisor: AstraZeneca, Daiichi Sankyo, Eisai, Shionogi, Kyowa-Kirin, Nippon-Kayaku, Novartis, Eli Lilly, Taiho, Chugai, Pfizer. M. Yamaguchi: Financial Interests, Personal, Speaker, Consultant, Advisor: AstraZeneca, Daiichi Sankyo, Eisai, Kyowa-Kirin, Nippon-Kayaku, Eli Lilly, Taiho, Chugai, Pfizer. T. Sangai: Financial Interests, Personal, Speaker, Consultant, Advisor: Chugai, Novartis, MSD, Taiho, Eisai, Maruho, PDRadiopahrma, Nippon-Kayaku, Kyowa-Kirin, AstraZeneca, Eli Lilly, Daiichi Sankyo, Pfizer; Financial Interests, Institutional, Funding: Taiho. T. Ishida: Financial Interests, Personal, Speaker, Consultant, Advisor: Pfizer, Chugai. M. Futamura: Financial Interests, Personal, Speaker, Consultant, Advisor: Daiichi Sankyo, Taiho, Chugai, Eisai, Eli Lilly, Nippon-Kayaku. N. Kosaka: Financial Interests, Personal, Stocks/Shares: Pfizer; Financial Interests, Personal, Full or part-time Employment: Pfizer. N. Masuda: Financial Interests, Personal, Speaker, Consultant, Advisor: Chugai, Pfizer, AstraZeneca, Eli Lilly, Daiichi -Sankyo; Financial Interests, Institutional, Funding: Chugai, Eli Lilly, AstraZeneca, Pfizer, Daiichi Sankyo, MSD, Eisai, Novartis, Sanofi, KyowaKirin, Nippon Kayaku. All other authors have declared no conflicts of interest.