a Department of Medical Oncology, Hospital de la Santa Creu i Sant Pau, Barcelona, Spain; Hereditary Endocrine Cancer Group, Human Cancer Genetics Programme, Spanish National Cancer Research Centre, Madrid, Spain; Department of Pathology, Fundacio Puigvert-University Autonomous, Barcelona, Spain; Department of Clinical Genetics, Erasmus MC, Rotterdam, the Netherlands; and Centro de Investigación Biomédica en Red de Enfermedades Raras (CIBERER), Madrid, Spain.
mTOR inhibitors are used to treat renal cell carcinoma (RCC). Treatment response is variable and appears to correlate with genetic alterations that activate mTOR signaling. Recently, everolimus was suggested to be more effective than sunitinib in chromophobe RCC (chRCC), a tumor with frequent mTOR pathway defects. This report presents the genomic and functional characterization of a metastatic chRCC that showed complete response at metastatic sites and 80% reduction in primary tumor size upon temsirolimus treatment. After surgery, the patient remained disease-free for 8 years after temsirolimus therapy. Whole-exome sequencing (WES) revealed 2 somatic variants in TSC2, a critical negative regulator of mTOR: a splicing defect (c.5069-1G>C) and a novel missense variant [c.3200_3201delinsAA; p.(V1067E)]. In vitro functional assessment demonstrated that the V1067E substitution disrupted TSC2 function. Immunohistochemistry in the tumor tissues revealed increased phosphorylated S6 ribosomal protein, indicating mTOR pathway activation. In conclusion, WES revealed TSC2 inactivation as the likely mechanism for this extraordinary response to temsirolimus. These findings support high efficacy of mTOR inhibitors in a subset of patients with chRCC and propose sequencing of mTOR pathway genes to help guide therapy.
Correspondence: Cristina Rodríguez-Antona, PhD, Hereditary Endocrine Cancer Group, Human Cancer Genetics Programme, Spanish National Cancer Research Centre (CNIO), Melchor Fernández Almagro 3, 28029 Madrid, Spain. Email: firstname.lastname@example.org; and Pablo Maroto, MD, Department of Oncology, Hospital de la Santa Creu i Sant Pau, Carrer de Sant Quintí, 89, 08026 Barcelona, Spain. Email: JMaroto@santpau.cat