Abstract P2-14-08: The Pilot Trial of Intermittent Exemestane Therapy for Metastatic Breast Cancer

Background: While aromatase inhibitors are effective for ER/PR positive breast cancer, resistance frequently develops. EXE is a steroidal AI and has a weak hormone-like activity. Long-term EXE treatment up-regulated amphiregulin-mediated EGFR activation and EXE resistance could result from ER-EGFR cross-talk. In cell culture and animal studies, acquired resistance to EXE was significantly delayed with intermittent use, associated with decreased production of amphiregulin. For first line therapy in MBC, EXE had a median progression free survival (PFS) of 10 mos. As second and third line therapies, PFS decreased to 4.7 mos and 2 mos, respectively. After ≥ 2 of prior endocrine therapy, PFS to EXE ranged between 3.4 mos to 3.7 mos. The rationale for this study was that after long-term estrogen deprivation clinically equivalent to long-term exposure to AI, estrogen may induce apoptosis. With intermittent EXE use, we hope to delay the acquired AI resistance. Methods: Aims were to: 1) assess the PFS and 2) compete response (CR), partial response (PR) and clinical benefit rate [CBR=CR +PR + Stable disease (SD)≥ 6 mos], assessment of toxicity, compliance with medication adherence, and quality of life with assessment of bone health. The study included: 1) ER/PR positive MBC in first, second line/third line hormonal therapy, and one prior chemotherapy for MBC with no prior EXE allowed. EXE was given 25 mg daily × 14 days then 7 days off treatment, each 21-day cycle, imaging was done after every three cycles. Correlatives with estradiol level were drawn at day 1 and day 15 in each cycle. Results: From June 2008 to 2012 we enrolled 33 MBC patients ER/PR positive MBC with a median age of 60 yrs (42–79). At this cut off data date, 2 were inevaluable due to incidental colon cancer and change in treatment choice. 17 patients received treatment as first line (52%), 10 as second or third line hormonal therapy (30%), and 6 who received chemotherapy for MBC (18%). Median PFS and (95% CI) was 6.2 mos (1.9–12.2), 4.2 mos (2.1–10.1), and 3.2 mos (2.1-NR), respectively. For first line patients, there were 3 PRs and 4 with SD>6 mos for a CBR of 7/14 (50%). For second/third line, there were 3 with SD>6 mos for a CBR of 3/9(33%), no response seen in the prior chemotherapy group. The major metastatic sites included bone, liver, lung. 4 patients were Her2+ (13%). Adverse effects including hot flashes (62%), insomnia (31%), nausea (24%), bone pain (17%), fatigue (41%), joint pain (31%) were observed. Median number of cycles delivered is 6 (2–24) for first line, 5.5 (1–15) for second/third line, and 5 (2–9) for prior chemotherapy. Correlatives and QOL assessments are ongoing. Conclusions: Compared to the standard continuous EXE, PFS and CBR is inferior in the intermittent EXE as first line therapy, as second and third line therapy, the median PFS was 4.2 comparable to reported 3.7 mos with the CBR was 33% to 31.5% observed in the EFFECT trial. Interestingly, hot-flash rate was much higher at 62% compared to 11.2% in the EFFECT trial. Arthralgia is comparable at 31%. Patients who already received chemotherapy do not appear to respond favorably to intermittent hormonal therapy. Full response data with correlatives regarding the estradiol levels will be presented. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P2-14-08.