Background: Premenopausal, high-risk, hormone receptor-positive breast cancer patients areoften treated with ovarian suppression in combination with aromatase inhibitors (AI). Thiscombination results in important adverse effects, particularly in sexual function, such as vaginaldryness and loss of libido. Vaginal estrogen is effective but may elevate serum estradiol levelsand, theoretically, may increase recurrence risk. Vaginal testosterone is also commonlyprescribed to ameliorate symptoms, though its safety remains uncertain, with limited availabledata. In our study, we aimed to determine the safety and efficacy, particularly regarding sexualfunction, of a low-dose, topical testosterone gel administration.Methods: This is a pilot, single-center study, designed to evaluate the efficacy of topicaltestosterone gel (3 mg/ml/per day) in improving sexual function in 30 premenopausal patientson ovarian suppression in combination with an AI. The primary safety endpoint was todetermine serum estradiol, measured by liquid chromatography mass spectrometry (E2) on amonthly a basis for 3 consecutive months. The primary efficacy endpoint was assessed by meansof the Female Sexual Function Index (FSFI) questionnaire, that include various domains of sexualfunction such as libido, sexual satisfaction and vaginal lubrication. The score can range from 2to 36, being 2 the lowest and 36 the highest sexual satisfaction. Patients had to have a baselineE2 of less than 2.7 pg/ml prior to study entry.Results: Herein, we report the preliminary results on the first 20 patients. The mean age was39.3 years, 85% had early or locally advanced disease and 15% had metastatic disease. Tenpatients completed the 3-month treatment, while five are still on therapy. Four of the 20discontinued treatment, mainly due to logistical difficulties during the follow-up visits. Onepatient had a localized allergic reaction and, also, discontinued treatment. A total of 15 patientsmaintained the value of E2 of less than 2,7 pg/ml during the 3-month treatment in all 3measurements. We observed an improvement in FSFI measures over the visits, with an increasefrom a mean of 10.2 at baseline to 19.4 at the third month (P<0.001), with the greatestimprovement observed between the second and third months.Conclusion: Our preliminary findings suggest that topical testosterone appears safe andeffective in improving sexual function in patients on ovarian suppression and aromataseinhibitor. Further studies are clearly warranted.

Citation Format: Patrícia Taranto, Diogo de Brito Sales, Luciano de Melo Pompei, Alessandro Leal, Gustavo Schvartsman, Antonio Carlos Buzaid. Safety and efficacy of low dose topical testosterone for sexual function improvement in women with breast cancer under treatment with ovarian suppression and aromatase inhibitor [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P4-10-05.