Background: The development of new combinations with mTOR inhibitors and the description of meaningful responses in cases with mutations in the mTOR pathway have raised the interest on these compounds. Predictive biomarkers of activity are crucial to ensure patients likely to benefit are properly treated. Methods: Through an observational prospective study by the Spanish Oncology Genitourinary Group (SOGUG), FFPE tumor samples were collected from 77 RCC patients treated with temsirolimus or everolimus. Patients with partial response (by RECIST), or stable disease for at least 6 months were classified as responders. Immunositochemistry (IHC) was performed in 64 patients for p-S6, p-S6K1, p-AKT, p21, BAP1 and PBRM1. Mutational analysis of key genes in mTOR pathway was performed through Next Generation Sequencing in tumor DNA. The association between expression of the proteins and response to mTOR inhibitors was analyzed through logistic regression. Results: The 77 patients studied had been treated with everolimus (79%) or temsirolimus (21%); 87% had ccRCC histology, 60% had intermediate, 39% good prognosis, and 1% poor prognosis (MSKCC); 29 patients were responders, 47 non-responders and 1 could not be classified. Among the five cases with mTOR pathway activating mutations (1 TSC1 (p.P333HfsTer5), 1 TSC2 (p.L826M); and 3 MTOR mutations (p.S2215_L2216delinsF, p.Y1974H, p.E773D)), three were responder patients and two non-responders. Regarding p-S6 staining, two responder patients and one non-responder had positive staining, while one responder had negative staining and one non-responder was not evaluable. In the full series, negative IHC expression for BAP1 and PBRM1 was associated with better mTOR inhibitor response (OR = 4.0, 95%CI = 1.4-11.9, P = 0.011 and OR = 3.9, 95%CI = 1.2-12.8, P = 0.025, respectively, multivariable analysis). However, no association between for p-S6, p-S6K1, p-AKT and p21 staining and mTOR inhibitor response was observed. Conclusions:TSC1, TSC2 and MTOR mutations only partially correlated with response. Lack of BAP1 and PBRM1 expression was associated with improved response to mTOR inhibitors.