Abstract P5-12-07: Hormone dynamics, pharmacokinetics, safety and efficacy of leuprorelin acetate 6-month depot formulation and tamoxifen adjuvant endocrine therapy combination in premenopausal patients with hormone receptor-positive breast cancer:

Background: Luteinizing hormone-releasing hormone agonist + tamoxifen is standard postoperative adjuvant endocrine therapy for premenopausal patients with hormone receptor-positive breast cancer. Postoperative adjuvant endocrine therapy is now used for a longer period, and the longer-lasting leuprorelin acetate 6-month depot formulation (TAP-144-SR[6M]) is expected to increase patients9 quality of life and decrease medical practitioners9 burden. Methods: The hormone dynamics, pharmacokinetics (PK), safety, and efficacy of TAP-144-SR(6M) were compared with those of the 3-month depot formulation (TAP-144-SR[3M]) in a 96-week, phase 3 open-label parallel-group comparison study in premenopausal breast cancer patients after surgery (ClinicalTrial.gov ID: NCT01546649). Inclusion criteria were estrogen receptor (ER) and/or progesterone receptor (PgR) positive; TNM classification of T1-T3, any N, M0; and premenopausal (menstruation confirmed within the previous 12 weeks or both follicle-stimulating hormone [FSH] 2 ] ≥10 pg/mL at enrollment). Patients were randomized to TAP-144-SR(6M) (6M group [6MG]) or TAP-144-SR(3M) (3M group [3MG]) based on number of axillary lymph node metastases, tumor size, age, ER/PgR status, chemotherapy or not, and study site. The primary endpoint was serum E 2 suppression rate based on the menopausal level (≤30 pg/mL) from 4 to 48 weeks after the first administration. Secondary endpoints were serum hormone dynamics, efficacy (disease-free survival [DFS] and distance DFS [DDFS]), PK and safety. The planned number of patients was 164 (82 in each group). Results: A total of 180 patients were enrolled from Apr 2012 to Feb 2013 and 167 patients were randomized. We compared 83 patients in 6MG (age: mean 44.2; SD 4.90) and 84 patients in 3MG (44.0; 5.18). There were no significant differences in background factors between the groups. 6MG showed non-inferior suppression of serum E 2 levels to 3MG (See Table). Serum LH and FSH levels were also decreased. DFSs and DDFSs at 96 weeks after randomization were similar in both groups. A double-peak PK profile and sustainable release of the study drug for 24 weeks were found with 6MG. All-grade adverse events (AEs) occurred in 98.8% and 97.6% and grade 3 or higher AEs in 18.1% and 21.4% with 6MG and 3MG, respectively. There were no significant differences in lumbar spine bone mineral density change rates in both groups. Conclusion: This first clinical study of TAP-144-SR(6M) in premenopausal breast cancer patients showed clinically noninferior serum E 2 suppression levels to TAP-144-SR(3M), and no significant safety differences between the groups. TAP-144-SR(6M) was confirmed to have excellent usability in premenopausal breast cancer patients after surgery, and is considered valuable for the appropriate treatment of these patients. Citation Format: Kurebayashi J, Toyama T, Sumino S, Fujimoto T. Hormone dynamics, pharmacokinetics, safety and efficacy of leuprorelin acetate 6-month depot formulation and tamoxifen adjuvant endocrine therapy combination in premenopausal patients with hormone receptor-positive breast cancer. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P5-12-07.