Background: Preclinical studies suggest that combining vandetanib (VAN), a multi-tyrosine kinase inhibitor of rearranged during transfection (RET) proto-oncogene, vascular endothelial growth factor receptor (VEGFR), and epidermal growth factor receptor (EGFR), with everolimus (EV), a mammalian target of rapamycin (mTOR) inhibitor, may improve antitumor activity. We determined the safety, maximum tolerated dose (MTD), recommended phase II dose (RP2D), and dose-limiting toxicities (DLTs) of VAN + EV in patients with advanced solid cancers and the effect of combination therapy on cancer cell proliferation and intracellular pathways., Patients and Methods: Patients with refractory solid tumors were enrolled in a phase I dose-escalation trial testing VAN (100-300 mg orally daily) + EV (2.5-10 mg orally daily). Objective responses were evaluated using RECIST v1.1. RET mutant cancer cell lines were used in cell-based studies., Results: Among 80 patients enrolled, 72 (90%) patients were evaluable: 7 achieved partial response (PR) (10%) and 37 had stable disease (SD) (51%; duration range: 1-27 cycles). Clinical benefit (SD or PR ≥ 6 months) was observed in 26 evaluable patients [36%, 95% confidence intervals (CI) (25% to 49%)]. In 80 patients, median overall survival (OS) was 10.5 months [95% CI (8.5-16.1)] and median progression-free survival (PFS) 4.1 months [95% CI (3.4-7.3)]. Six patients (7.5%) experienced DLTs and 20 (25%) required dose modifications. VAN + EV was safe, with fatigue, rash, diarrhea, and mucositis being the most common toxicities. In cell-based studies, combination therapy was superior to monotherapy at inhibiting cancer cell proliferation and intracellular signaling., Conclusions: The MTDs and RP2Ds of VAN + EV are 300 mg and 10 mg, respectively. VAN + EV combination is safe and active in refractory solid tumors. Further investigation is warranted in RET pathway aberrant tumors., Competing Interests: Disclosure TC: speaker's fees from Society for Immunotherapy of Cancer and Bristol Myers Squibb; consulting/advisory role fees from MedImmune/AstraZeneca, EMD Serono, and Bristol Myers Squibb, research funding to MD Anderson Cancer Center from Boehringer Ingelheim, MedImmune/AstraZeneca, and Bristol Myers Squibb. SAP-P: research/grant funding (institutional) from AbbVie, Inc.; Aminex Therapeutics; Amphivena Therapeutics, Inc.; BioMarin Pharmaceutical, Inc.; Boehringer Ingelheim; Bristol Myers Squib; Cerulean Pharma Inc.; Chugai Pharmaceutical Co., Ltd.; Curis, Inc.; Five Prime Therapeutics; Genmab A/S; GlaxoSmithKline; Helix BioPharma Corp.; Incyte Corp.; Jacobio Pharmaceuticals Co., Ltd.; Medimmune, LLC; Medivation, Inc.; Merck Sharp and Dohme Corp.; NewLink Genetics Corporation/Blue Link Pharmaceuticals; Novartis Pharmaceuticals; Pieris Pharmaceuticals, Inc.; Pfizer; Principia Biopharma, Inc.; Puma Biotechnology, Inc.; Rapt Therapeutics, Inc.; Seattle Genetics; Syneos Health; Taiho Oncology; Tesaro, Inc.; TransThera Bio; and Xuanzhu Biopharma. DSH: research/grant funding from AbbVie, Adaptimmune, Aldi-Norte, Amgen, Astra-Zeneca, Bayer, BMS, Daiichi Sankyo, Eisai, Fate Therapeutics, Genentech, Genmab, Ignyta, Infinity, Kite, Kyowa, Lilly, LOXO, Merck, MedImmune, Mirati, miRNA, Molecular Templates, Mologen, NCI-CTEP, Novartis, Pfizer, Seattle Genetics, Takeda, and Turning Point Therapeutics; funding for travel, accommodations, and expenses from Bayer, LOXO, miRNA, Genmab, AACR, ASCO, and SITC; consultant/advisor for Alpha Insights, Amgen, Axiom, Adaptimmune, Baxter, Bayer, Genentech, GLG, Group H, Guidepoint, Infinity, Janssen, Merrimack, Medscape, Numab, Pfizer, Prime Oncology, Seattle Genetics, Takeda, Trieza Therapeutics, WebMD; ownership interests in Molecular Match (Advisor), OncoResponse (Founder), Presagia Inc. (Advisor). SF: clinical trial research support through the institution from NIH/NCI; AstraZeneca; Abbisko; Anaeropharma Science; Arrien Pharmaceuticals; BeiGene; BioAtla, LLC; Boehringer Ingelheim; Eli Lilly & Co.; Hookipa Biotech; Huya Bioscience International; IMV, Inc.; Innovent Biologics, Co., Ltd.; Lyvgen Biopharma, Co., Ltd.; MacroGenics; Medivir AB; Millennium Pharmaceuticals, Inc.; Nerviano Medical Sciences; Neupharma, Inc.; Novartis; OncoMed Pharmaceuticals; Parexel International, LLC; Sellas Life Sciences Group; Soricimed Biopharma, Inc.; Tolero Pharmaceuticals; NovoCure; Turnstone Biologics; Taiho Oncology; and NCCN. AN: Research funding from NCI, EMD Serono, MedImmune, Healios, Atterocor, Amplimmune, ARMO BioSciences, Eli Lilly, Karyopharm Therapeutics, Incyte, Novartis, Regeneron, Merck, BMS, Pfizer, CytomX Therapeutics, Neon Therapeutics, Calithera Biosciences, Top Alliance Biosciences, Kymab, PsiOxus, Arcus Biosciences, NeoImmuneTech, ImmuneOncia, Surface Oncology; on advisory board of CytomX Therapeutics, Novartis, and Genome & Company, OncoSec KEYNOTE-695, STCube Pharmaceuticals, Kymab; travel and accommodation expense from ARMO BioSciences. Spouse: Research funding from Immune Deficiency Foundation, Jeffery Modell Foundation and Chao Physician-Scientist, and Baxalta; advisory board from Takeda, CSL Behring, Horizon Pharma. FJ: grant/research funding (institutional) from Novartis, Genentech, Biomed Valley Discoveries, Plexxikon, Deciphera, PIQUR Therapeutics, Symphogen, Bayer, Fujifilm Corporation and Upsher-Smith Laboratories, Astex, Asana, Astellas, Agios, Proximagen, and Bristol Myers Squibb; advisory board member for Deciphera, IFM Therapeutics, Synlogic, Guardant Health, IDEAYA, PureTech Health, and Jazz pharmaceuticals; consultant fees from Trovagene, Immunomet, Primmune Therapeutics, Jazz Pharmaceuticals, and SOTIO; ownership interests in Trovagene. GSF: research funding from 3-V Biosciences, AbbVie, ADC Therapeutics, Aileron, American Society of Clinical Oncology, Amgen, ARMO, AstraZeneca, BeiGene, BioAtla, Biothera, Celldex, Celgene, CicloMed, Curegenix, Curis, Cyteir, Daiichi, Delmar, eFFECTOR, Eli Lilly, EMD Serono, Exelixis, Fujifilm, Genmab, GlaxoSmithKline, Hutchison MediPharma, Ignyta, Incyte, Jacobio, Jounce, Kolltan, LOXO, MedImmune, Millennium, Merck, miRNA Therapeutics, National Institutes of Health, Novartis, OncoMed, Oncothyreon, Precision Oncology, Regeneron, Rgenix, Ribon, Strategia, Syndax, Taiho, Takeda, Tarveda, Tesaro, Tocagen, Turning Point Therapeutics, U.T. MD Anderson Cancer Center, VEGENICS, and Xencor; advisor fees from Fujifilm and EMD Serono; royalties from Wolters Kluwer; funding for travel from Bristol Myers Squibb, EMD Serono, Fujifilm, Millennium, and Sarah Cannon Research Institute; speaker's bureau fees from Total Health Conferencing. APC: consultant fees from Deciphera Pharmaceuticals, Guidepoint Global, Genentech, Inc., Bayer Healthcare Pharmaceuticals, OncLive, Novartis Pharmaceuticals, and Ignyta, Inc.; speaker fees from Medscape. SIS: research support from Exelixis; consultant fees from Fortress Biotech and LOXO oncology; honoraria from Eisai. FM-B: Consulting fees from Aduro Biotech Inc., Alkermes, AstraZeneca, Debiopharm, eFFECTOR Therapeutics, F. Hoffman-La Roche Ltd., Genentech Inc., IBM Watson, Jackson Laboratory, Kolon Life Science, OrigiMed, PACT Pharma, Parexel International, Pfizer Inc., Samsung Bioepis, Seattle Genetics Inc., Tyra Biosciences, Xencor, Zymeworks; advisory committee fees from Immunomedics, Inflection Biosciences, Mersana Therapeutics, Puma Biotechnology Inc., Seattle Genetics, Silverback Therapeutics, Spectrum Pharmaceuticals, Zentalis; sponsored research from Aileron Therapeutics, Inc., AstraZeneca, Bayer Healthcare Pharmaceutical, Calithera Biosciences Inc., Curis Inc., CytomX Therapeutics Inc., Daiichi Sankyo Co. Ltd., Debiopharm International, eFFECTOR Therapeutics, Genentech Inc., Guardant Health Inc., Klus Pharma, Millennium Pharmaceuticals Inc., Novartis, Puma Biotechnology Inc., Taiho Pharmaceutical Co.; honoraria from Chugai Biopharmaceuticals, Mayo Clinic, Rutgers Cancer Institute of New Jersey; other (Travel Related) from Beth Israel Deaconess Medical Center. JVH: research support from AstraZeneca, GlaxoSmithKline, and Spectrum; consultant/advisory board member for AstraZeneca, Boehringer Ingelheim, Catalyst, Genentech, GlaxoSmithKline, Guardant Health, Foundation medicine, Hengrui Therapeutics, Eli Lilly, Novartis, Spectrum, EMD Serono, Sanofi, Takeda, Mirati Therapeutics, BMS, BrightPath Biotherapeutics, Janssen Global Services, Nexus Health Systems, EMD Serono, Pneuma Respiratory, Kairos Venture Investments, Roche, Leads Biolabs; royalties and patents from Spectrum. VS and IMS: research funding/grant support from Novartis, GlaxoSmithKline, Nanocarrier, Vegenics, Celgene, Northwest Biotherapeutics, Berg Health, Incyte, Fujifilm, PharmaMar, D3, Pfizer, MultiVir, Amgen, AbbVie, Alfa-sigma, Agensys, Boston Biomedical, Idera Pharma, Inhibrx, Exelixis, Blueprint medicines, LOXO oncology, MedImmune, ALTUM, Dragonfly therapeutics, Takeda, and Roche/ Genentech, National Comprehensive Cancer Network, NCI-CTEP, and UT MD Anderson Cancer Center; consultant/advisory board for Helsinn, LOXO Oncology/ Eli Lilly, R-Pharma US, INCYTE, QED pharma, MedImmune, Novartis; funding for travel from Novartis, PharmaMar, ASCO, ESMO, Helsinn, Incyte. All other authors have declared no conflicts of interest. Data sharing The data supporting the findings presented in this manuscript are available upon reasonable academic request to the study principal investigator (VS)., (Copyright © 2021 The Authors. Published by Elsevier Ltd.. All rights reserved.)