Abstract P4-07-22: Real world effectiveness of overall survival (OS) with palbociclib (PAL) plus (+) endocrine therapy (ET) in hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2-) advanced breast cancer (ABC) patients in Japan

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Abstract Introduction: PAL, cyclin-dependent kinases 4 and 6 inhibitor (CDK4/6i), + ET is a standard therapy for the treatment of HR+/HER2- ABC. Efficacy and safety of PAL + ET was shown by two randomized clinical trials, PALOMA-2 and PALOMA-3. Further, recent large real-world studies revealed effectiveness of PAL + aromatase inhibitor (AI) for HR+/HER2- ABC in routine United States clinical practice. To strengthen the real-world evidence (RWE) of PAL + ET for HR+/HER2- ABC treatment under different clinical practice and healthcare situations, we conducted observational study to evaluate the effectiveness of PAL + ET in Japanese real-world setting. Recently, we reported that the median (95% CI) OS were 68.2 months (60.8-not estimated (NE)), among patients who treated with PAL + ET in 1st line (1L) in Japanese routine clinical practice with longer follow-up after interim analysis. Here, we investigate the subgroup of real-world OS of Japanese patients treated with PAL + ET as 1L for HR+/HER2- ABC to understand the impact of OS. Methods: In this multicenter, observational study, patients with HR+/HER2- ABC, who initiated PAL + ET from 15 December 2017 (launch date in Japan) to 31 December 2020 were enrolled. To reduce selection bias, all patients who started PAL during the above period were listed up and eligibility was confirmed. Key eligibility criteria were: 1) Diagnosis of HR+/HER2- ABC; 2) Patients received PAL + ET in 1L or 2L; 3) Patients had at least 6 months of follow up from start of PAL or died within that period. The primary endpoint was real-world progression free survival (rwPFS), and one of the secondary endpoints was OS, defined as the time from start of PAL + ET treatment to death due to any cause. We performed the further analysis, including subgroup analysis, about OS of 1L PAL + ET to investigate what factors could affect its clinical benefits. Results: In this study, 693 patients from 20 study sites in Japan were enrolled. Among them, 426 and 267 received PAL + ET as 1L and 2L, respectively. The median age was 60.0 (range 29-87) and 482 patients (70.0%) were postmenopausal. 54.0% patients had visceral involvement and 43.3% had <12 months of treatment-free interval (TFI; defined as end date of adjuvant therapy to diagnosis date of recurrence). 295 patients received subsequent therapy out of 426 patients after PAL + ET as 1L. 60.7% (179/295) of patients received an endocrine-based regimen as first subsequent treatment; of those 23.1% (68/295) received CDK4/6i + ET, 19.3% (57/295) endocrine monotherapy, and 17.6% (52/295) ET + everolimus. After a median follow-up of 48.1 months, the following subgroup analysis was performed for OS in 1L, showing median OS (95% CI) and, survival rate at 60 months: pre-/post-menopausal status was not reached (NR) (59.4-NE), 61.3%/68.0 months (58.5-NE), 55.6%, TFI<12 months/TFI12>months/De novo metastatic was 56.3 months (43.9-68.2), 46.1%/NR (NE-NE), 72.9%/NR (56.3-NE), 60.0%, visceral/non-visceral metastasis was 65.0 months (56.3-NE), 52.3%/NR (63.2-NE), 61.3%, liver metastasis was 46.4 months (37.2-NE), 42.8%, and bone only disease was NR (57.8-NE), 61.2%. Conclusions: The findings of the study based on Japanese routine clinical practice further confirmed that the clinical benefits of PAL+ET is consistent regardless of patient characteristics in the real-world setting. In all subgroup other than TFI<12 months or liver metastasis, median OS was >5 years with 1L PAL + ET, underlining the use of PAL + ET as 1L standard for ABC in the real-world setting. Citation Format: Michiko Tsuneizumi, Tetsuhiro Yoshinami, Shigenori E. Nagai, Masaya Hattori, Hiroko Masuda, Takuho Okamura, Kenichi Watanabe, Takahiro Nakayama, Daisuke Takabatake, Michiko Harao, Hiroshi Yoshino, Natsuko Mori, Hiroyuki Yasojima, Chiya Oshiro, Madoka Iwase, Miki Yamaguchi, Takafumi Sangai, Shinsuke Sasada, Takanori Ishida, Manabu Futamura, Nobuyoshi Kosaka, Yasuaki Muramatsu, Norikazu Masuda. Real world effectiveness of overall survival (OS) with palbociclib (PAL) plus (+) endocrine therapy (ET) in hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2-) advanced breast cancer (ABC) patients in Japan [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2024; 2024 Dec 10-13; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2025;31(12 Suppl):Abstract nr P4-07-22.

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