AbstractBackground: Aromatase inhibitors are a mainstay hormone receptor-positive breast cancer treatment. AIA occur in up to 50% of patients (pts), adversely affecting quality of life and treatment compliance. A small phase II clinical trial of oral testosterone unedeconate appeared to improve AIA over placebo (P), with no significant androgenic side effects. The current study was performed to confirm these findings.Methods: This randomized P-controlled trial enrolled postmenopausal women on adjuvant anastrozole or letrozole and experiencing moderate-to-severe AIA (≥5 on 0-10 scale). Pts were initially randomized to receive a subcutaneous pellet containing T 120 mg + anastrozole 8 mg (T+AIpellet) or P at the end of the first week on study (after obtaining baseline hot flash data) and at 3 months (mo). Due to slow accrual, the protocol was amended to change the route of delivery to topical T or P applied to the skin once daily for 6 mo. Baseline and monthly questionnaires were administered, including: Modified Brief Pain Inventory for aromatase arthralgia (BPI-AIA), prolife of mood states (POMS), the menopause specific quality of life questionnaire (MENQOL), a hot flash diary, the hot flash related daily interference scale (HFRDIS) and a symptom experience questionnaire. The primary endpoint was intra-patient change in joint pain at 3 mo, compared using a two-sample t-test.Results: 227 pts were accrued between 9/1/2013-11/29/2017. 55 pts were randomized prior to the protocol amendment and received T+AIpellet or P. Baseline characteristics were balanced between arms, with the exceptions of median weight, BMI, hemoglobin (all higher in T arm), and breast tenderness, dissatisfaction with personal life/depression, and skin changes (all higher in P arm). Compared to baseline, there were no significant differences between T and P in average pain or joint stiffness at 3 (p=0.483) or 6 mo (p=0.573). Average pain was significantly lower each month compared to baseline, irrespective of treatment arm. There were no significant differences in any other items evaluated by BPI-AIA, POMS, MENQOL, hot flash diary or HFRDIS. Similarly, there were no substantial differences in toxicity. A subset analysis of the 55 pts randomized to receive T+AIpellet or P identified significant reductions in average pain scores with T+AIpellet during the first month (p=0.038), but not thereafter. T+AIpellet pts had significantly more reduction in reported % of baseline hot flash frequency (p=0.034) and score (p=0.031), nausea (p=0.019), fatigue (p=0.042), mood swings (p=0.026), hand/feet swelling (p=0.009), stress urinary incontinence (p=0.039) and changes in appearance, texture or tone of their skin (p=0.0083), than pts on P.Conclusions: Overall, T did not improve AIA or menopausal symptoms compared to P. While there was significant improvement in AIA over the study period, T did not facilitate this process. However, T+AIpellet was associated with improvement in short-term AIA and several menopausal symptoms compared to P, suggesting that subcutaneous T combined with anastrozole may be superior to transdermal T alone.Support: UG1CA189823, U10CA180820, U10CA189809; ClinicalTrials.gov Identifier: NCT01573442Citation Format: Leon-Ferre RA, Le-Rademacher J, Terstriep S, Glaser R, Novotni P, Giuliano A, Copur MS, Jones C, Page S, Mitchell W, Birrell SN, Loprinzi CL. A randomized, double-blind, placebo-controlled trial of testosterone (T) for aromatase inhibitor-induced arthralgias (AIA) in postmenopausal women: Alliance A221102 [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 P4-16-01.