Exceptional Response to Temsirolimus in a Metastatic Clear Cell Renal Cell Carcinoma With an Early Novel MTOR-Activating Mutation

mTOR pathway inhibitors are important drugs for the treatment of advanced renal cell carcinoma (RCC). However, no valid predictive markers have been identified to guide treatment selection and identify patients who are sensitive to these drugs. Mutations activating the mTOR pathway have been suggested to predict response; however, their predictive value is still unclear. Here, we present the genomic and functional characterization of a patient with metastatic clear cell RCC (ccRCC) who experienced a partial response to temsirolimus after a poor response to 2 previous lines of treatment. At the time of publication, the patient was disease-free 8 years after temsirolimus treatment. Multiregion whole-exome sequencing (WES) on 3 regions of the primary tumor, 1 metastasis, and blood revealed tumor mutations in driver genes in ccRCC: a missense mutation in VHL (p.W88L), a loss-of-function mutation in BAP1 (p.E454Rfs*15), and a novel missense mutation in MTOR (p.Y1974H). The MTOR mutation was present in all tumor regions, with similar allele frequency as the VHL mutation, and in vitro functional assessment of the MTOR variant demonstrated that it increased mTORC1 activity. Consistently, immunohistochemistry in the tumor samples demonstrated increased levels of phospho-S6. In conclusion, multiregion WES identified a novel MTOR mutation acquired early during tumor development as the event leading to a high sensitivity to temsirolimus treatment. This study supports tumor multiregion sequencing to detect truncal mutations in the mTOR pathway to identify patients sensitive to mTOR inhibitors.

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