Background: In early ER+ breast cancer, neo-adjuvant (NA) endocrine therapy (ET) may identify a subset of patients with endocrine sensitive disease with excellent outcomes without chemotherapy. In patients receiving a NA aromatase inhibitor, on- therapy, short term (day 14) Ki-67 of <10% and post NA pre-operative endocrine prognostic index (PEPI) 0 at surgery are associated with low relapse rates without chemotherapy. Ribociclib, a novel CDK4/6 inhibitor is active in ER+ metastatic breast cancer. We hypothesize that ribociclib+letrozole as NA ET for stage II-III breast cancer will increase the number of women with a PEPI 0 at surgery. Trial Design: Randomized, placebo-controlled, multi-center, phase II, investigator initiated trial of NA letrozole +/- ribociclib in postmenopausal women with ER+, HER2-, breast cancer. Subjects will be randomized 1:1:1 to letrozole 2.5 mg daily + placebo, letrozole 2.5mg daily + ribociclib 600mg daily on D1-21 of a 28 day cycle (intermittent dosing), or letrozole 2.5mg daily + ribociclib 400mg daily (continuous dosing). Treatment will be continued for 6 months followed by surgery. Research core biopsies and blood will be collected at baseline, at day 14, and at surgery. A Ki67 >10% at day 14 will result in discontinuation of the subject from the protocol as this may be an early indicator of resistance to endocrine therapy. An MRI will be done after 2 months of therapy to assess response/progression. Primary endpoint is a PEPI score of 0 at surgery. Key Eligibility Criteria: Postmenopausal (natural or surgical) women with stage II/III ER+, HER2- breast cancer. Must have a palpable breast mass of at least 2 cm. Multicentric/contralateral invasive disease not allowed. Ipsilateral/contralateral DCIS is allowed. Inflammatory breast cancer is excluded. Specific Aims: Primary objective: To determine if ribociclib+letrozole as a 24 week NA ET increases rate of PEPI score of 0 at surgery compared to letrozole. Secondary objectives: To determine if ribociclib+letrozole as a 24 week NA ET increases the proportion of tumors with complete cell cycle arrest compared to letrozole; to determine if ribociclib in combination with letrozole for 24 weeks results in improved 5 year RFS compared to letrozole; to examine differences in response rates between the two ribociclib containing arms vs letrozole. Statistical Methods: The two ribocilib containing arms (n=80) will be combined for analysis against placebo + letrozole (n=40). Assuming that addition of ribociclib will increase the rate of PEPI 0 by 20%, and setting Type I error rate at 10% and Type II error rates at 20% in the final analysis, a sample size of 80 women in the treatment arms (40 in each arm) and 40 women in the control arm are needed to show significance. Patient accrual and target accrual: Participating sites include The Univ of Kansas Med Ctr, City of Hope National Med Ctr, Massachusetts General Hospital, University of Miami Sylvester Comprehensive Cancer Ctr, University of Arkansas for Medical Sciences, and University of Wisconsin. The trial has accrued 16 patients with a target accrual of 120 patients. Accrual should be complete in 2/2017. Contact information: Qamar Khan, MD (qkhan@kumc.edu). Citation Format: Khan QJ, Prochaska LH, Mohammad J, Yuan Y, O'Dea A, Bardia A, Wisinski K, Hard M, Baccaray S, Makhoul I, Wagner J, Laura S, Ma C, Sharma P. Femara plus ribociclib or placebo as neo-adjuvant endocrine therapy for women with ER+, HER2-negative early breast cancer - The Feline trial [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr OT3-02-06.

Background: To date, the use of anti-androgens in the subset of triple negative breast cancers (TNBC) that express androgen receptor (AR) has shown modest response rates, indicating anti-androgen-resistance in the majority of these tumors. Based on data that Cyclin D kinase (CDK) inhibitors reverse resistance to anti-androgens in prostate cancer cell lines, we hypothesize that the use of CDK inhibition may enhance the activity of anti-androgens in AR-positive TNBC. Methods: Key eligibility include: patients with centrally confirmed AR-positive TNBC, defined as AR expression >0%; 0 to 1 line of prior therapy for metastatic disease; and measurable disease. Patients are treated with bicalutamide 150mg orally once daily plus ribociclib at one of 3 dose levels (see table). Table 1Dose levelBicalutamideRibociclib1150mg orally once daily (D1 to 28)400mg daily (D1 to 21)2150mg orally once daily (D1 to 28)400mg daily (D1 to 28)3150mg orally once daily (D1 to 28)600mg daily (D1 to 21) Results: AR expression was positive by trial criteria in 74% of screened patients. Three patients have been accrued at each dose level. Median age is 56 and 6 and 3 patients were treated in first and second-line settings, respectively. Median AR expression was 50% (range 5 to 75%). Toxicity data is available for 6-patients treated on dose levels 1 and 2. No dose-limiting toxicities were noted. As anticipated with ribociclib, the most common toxicity is neutropenia (1 patient grade 4 and 2 patients grade 3). Two patients experienced grade 3 hypertension and 1 experienced grade 3 lymphopenia. Grade 2 or lower toxicities included fatigue, nausea, hyperglycemia and mucositis. One patient experienced grade 1 QT interval prolongation. Conclusion: The combination of bicalutamide and ribociclib is tolerable without unexpected toxicities. Data on the 3-patients treated at dose level 3 and dose expansion will be included. Phase 2 dosing schedule will be decided based on phase 1 results. Citation Format: Sharifi M, Wisinski KB, Burkard ME, Tevaarwerk AJ, Tamkus D, Chan N, Truica C, Danciu O, Hoskins K, O'Regan RM. Phase I trial of bicalutamide and ribociclib in androgen receptor-positive triple negative breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr OT1-02-01.