Palbociclib plus endocrine therapy versus capecitabine in premenopausal women with hormone receptor-positive, HER2-negative metastatic breast cancer (Young-PEARL): overall survival analysis of a randomised, open-label, phase 2 study.

backgroundThe phase 2 randomised Young-PEARL study demonstrated that palbociclib plus exemestane with ovarian function suppression significantly prolonged progression-free survival compared with capecitabine in premenopausal women with hormone receptor-positive, HER2-negative metastatic breast cancer. Here, we report results of the protocol-specified secondary endpoint of overall survival.

methodsYoung-PEARL was a multicentre, randomised, open-label, phase 2 study conducted at 14 institutions in South Korea. Premenopausal women aged 19 years or older with histologically confirmed hormone receptor-positive, HER2-negative metastatic breast cancer that recurred or progressed during or after previous tamoxifen treatment, who were aromatase inhibitor naive, and had an Eastern Cooperative Oncology Group performance status of 0-2 were eligible. One previous line of chemotherapy was permitted in the metastatic setting. Eligible patients were randomly assigned (1:1), using block randomisation (block size of two) stratified by previous chemotherapy for metastatic breast cancer and presence of visceral metastasis, to receive either palbociclib (orally, 125 mg per day on a 3-weeks-on, 1-week off schedule) plus exemestane (orally 25 mg daily) with leuprorelin (subcutaneously 3·75 mg on day 1 of each 28-day cycle) or capecitabine (orally, 1250 mg/m

findingsBetween June 15, 2016, and Dec 10, 2018, 189 patients were enrolled. 184 patients were randomly assigned to the palbociclib plus endocrine therapy group (n=92) or the capecitabine group (n=92), of whom 174 were included in the modified intention-to-treat population (n=90 in the palbociclib plus endocrine therapy group and n=84 in the capecitabine group). All patients were female and ethnicity data were not collected. As of data cutoff (Feb 29, 2024), median follow-up was 54·0 months (IQR 34·1-74·4). Median progression-free survival was 19·5 months (90% CI 14·3-22·2) for palbociclib plus endocrine therapy and 14·0 months (11·7-18·7) for capecitabine (hazard ratio 0·74 [90% CI 0·57-0·98]; one-sided log-rank p=0·036). 52 (58%) of 90 patients in the palbociclib plus endocrine therapy group and 48 (57%) of 84 in the capecitabine group died, with a median overall survival of 54·8 months (95% CI 48·9-77·1) in the palbociclib plus endocrine therapy group versus 57·8 months (46·3-89·2) in the capecitabine group (hazard ratio 1·02 [95% CI 0·69-1·51]; p=0·92). The most common grade 3 or worse adverse event was neutropenia (59 [64%] of 92 in the palbociclib plus endocrine therapy group vs 15 [18%] of 85 in the capecitabine group) . No treatment-related deaths occurred.

interpretationWith extended follow-up, palbociclib plus exemestane with ovarian function suppression continued to show a significant benefit in progression-free survival compared with capecitabine in premenopausal patients with hormone receptor-positive, HER2-negative metastatic breast cancer who had been previously treated with tamoxifen; however, no improvement in overall survival was seen. Given the progression-free survival benefit, the upfront use of palbociclib plus endocrine therapy is the preferred option for premenopausal women, although a capecitabine-first strategy might be an alternative treatment strategy for maintaining overall survival in resource-limited settings.

fundingPfizer and Ministry of Health & Welfare, South Korea.