AbstractBackgroundSunitinib is a multi‐target tyrosine kinase inhibitor (TKI) that inhibits VEGF receptor 1, 2, 3 (VEGFRs), platelet‐derived growth factor receptor (PDGFR), colony‐stimulating factor receptor (CSFR), and the stem cell factor receptor c‐KIT. Temsirolimus inhibits mammalian target of rapamycin (mTOR) through binding to intracellular protein FKBP‐12. Both agents are approved for the treatment of metastatic renal cell carcinoma (mRCC), have different anticancer mechanisms, and non‐overlapping toxicities. These attributes form the scientific rationale for sequential combination of these agents. The primary objective of the study was to investigate the efficacy of alternating sunitinib and temsirolimus therapy on progression‐free survival (PFS) in mRCC.MethodsWe undertook a phase II, multi‐center, single cohort, open‐label study in patients with mRCC. Patients were treated with alternating dosing of 4 weeks of sunitinib 50 mg PO daily, followed by 2 weeks rest, then 4 weeks of temsirolimus 25 mg IV weekly, followed by 2 weeks rest (12 weeks total per cycle). The primary endpoint was PFS. Secondary endpoints included clinical response rate and characterization of the toxicity profile of this combination therapy.ResultsNineteen patients were enrolled into the study. The median observed PFS (n= 13 evaluable for PFS) was 8.8 months (95% CI 6.8–25.2 months). Best responses achieved were five partial response, nine stable disease, and three disease progression according to RECIST 1.1 guidelines (two non‐evaluable). The most commonly observed toxicities were fatigue, platelet count decrease, creatinine increased, diarrhea, oral mucositis, edema, anemia, rash, hypophosphatemia, dysgeusia, and palmar‐plantar erythrodysesthesia syndrome.ConclusionAlternating sunitinib and temsirolimus did not improve the PFS in patients with mRCC.