Background: In multicenter randomized phase 2 study (FARETES) we showed that male patients with mRCC receiving targeted therapy had significantly less fatigue and better symptom control with testosterone undecanoate (T) (MASCC 2018, LBA004). Here we described exploratory endpoints in FARETES study. Methods: Sixty male patients with clear cell mRCC, normal PSA level, low testosterone level and no evidence of hypothyroidism receiving first-line sunitinib or pazopanib with fatigue were randomly assigned (1:1) to either T (Nebido, 1,000 mg) and targeted therapy or targeted therapy alone (control group). T was injected intramuscular deeply on Day 1 of a new treatment cycle. Exploratory endpoints included rate of adverse events (AE) of targeted therapy, duration of targeted therapy, objective response rate (ORR), progression-free survival (PFS) and overall survival (OS). Results: As of the data cutoff on October 17, 2018, median (range) follow-up was 15.2 (9.9 -16.5) months. No unexpected toxicity of T was observed. Grade 3-4 targeted therapy-related AE occurred in 11 (37%) and 3 (10%) patients in the control group and T group, respectively. Discontinuation due to AE was observed in 3% (1/30) of patients in the T group and in 17% (5/30) of patients in the control group. ORR and PFS were significantly better in the T group (all P < 0.05, Table). Median OS was not reached in either group. Clinical trial information: NCT03379012Conclusions: T therapy could decrease rate of serious AE of targeted therapy. Male mRCC patients receiving T had longer duration of targeted therapy, better PFS and ORR. Larger trials are needed to evaluate efficacy of T in this group of patients.