Background: Male breast cancer (MBC) is rare and accounts for 1% of all breast cancers. Much of the evidence to support the efficacy of CDKi come from clinical trials that have minimal male representation, either because they were excluded or because of very low accrual. Palbociclib in conjunction with aromatase inhibitors (AI) and fulvestrant has recently been approved in men for the treatment of advanced hormone receptor positive (HR+), HER2 negative breast cancer. A recent retrospective review of postmarketing reports and electronic health records showed the efficacy and safety profile of palbociclib in men may be similar to that of women. However, further studies are needed to support this conclusion. We set out to evaluate the response rate to palbociclib in a single institution known to see a high number of male breast cancer patients.

Methods: We identified male patients with metastatic breast cancer treated with palbociclib through the MD Anderson Cancer Center Breast Medical Oncology database. The primary objective was to evaluate response rate to palbociclib in male patients with HR +, HER 2 negative breast cancer. Descriptive statistics were used. Response was assessed based on radiographic RECIST criteria version 1.1

Results: We identified 26 men treated with palbociclib from 1/2015 to 4/2018. The median age of breast cancer diagnosis was 54 years (range 25-70). Five patients (19%) presented with de novo metastatic disease. 14 (54%) patients were treated in the first-line, 3 (12%) second-line, and 9 (35%) third-line or greater. Palbociclib was combined with AI+GNRH in 13 pts (50%), fulvestrant+GNRH in 4 pts (15%), letrozole alone in 3 pts (13%), and fulvestrant alone in 6 pts (23%). Response rate was assessed in 25 of the 26 patients. The rate of response was 48% (12 of 25 patients), with 1 patient achieving a complete response (CR), 11 achieving a partial response (PR), 6 with stable disease (SD) and 7 with progressive disease (PD). Response rate was 59% (10/17) for those that received palbociclib in their first or second lines of therapy while response rate was 25% (2/8) if received as third or higher line of therapy. Response rate was higher in those that received palbociclib with letrozole 62.5% (10/16) versus those who received it with fulvestrant 22.2% (2/9). The median duration of response was 3.8 months. The median follow up from initiation of palbociclib was 15 months. The median PFS for all patients was 10.8 months (IQR 4.9-24.5). Those who received 1-2 lines of therapy had a median PFS of 12.4 months (IQR 4.9-24.5), while the median PFS was 9.2 months for those who received 3 or more lines of therapy (IQR 5.0-14.1).

Conclusion: Palbociclib provides benefit for MBC patients with the majority of men in this study achieving clinical response to treatment.

Citation Format: Oluchi Oke, Jiangong Niu, Akshara Raghavendra, Mariana Chavez-McGregor, Hui Zhao, Debu Tripathy, Sharon Giordano. Palbociclib in advanced male hormone positive breast cancer [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 P4-17-02.