Background: BRAF V600E mutations are associated with aggressive biology and limited response to standard chemotherapy, especially during second-line and beyond therapies. BRAF V600E mutant and wild-type colorectal cancers (CRCs) differ in their expression profiles, and preclinical evidence suggests that microtubule inhibitors have an antitumour effect on xenograft models of BRAF V600E mutant CRCs. Eribulin has the best growth inhibitory activity in vitro of the microtubule inhibitors. Also, we have evidenced a hint of activity for patients with BRAF V600E mutant metastatic CRC (mCRC) with tumour shrinkage following eribulin treatment., Trial Design: The BRAVERY study is a multicentre phase II study to evaluate the efficacy and safety of eribulin in patients with BRAF V600E mutant mCRC detected in either tumour tissues (primary analysis part) or circulating tumour DNA assays (liquid biopsy part). Key eligibility criteria are refractoriness and intolerance to at least one regimen (including irinotecan or oxaliplatin) containing fluoropyrimidine and Eastern Cooperative Oncology Group performance status of 0-1. Eribulin is to be administered intravenously at a dose of 1.4 mg/m 2 on days 1 and 8 and repeated every 21 days. The primary endpoint is the confirmed objective response rate (ORR) by investigator's assessment. We calculated the sample size of the primary analysis part at 27 patients using a two-stage design with 25% ORR deemed promising and 5% unacceptable (one-sided α, 0.05; β, 0.1). Secondary endpoints include disease control rate, progression-free survival, overall survival and adverse events. Moreover, we will collect pretreated tissue and serial blood samples for biomarker analyses, focusing on gene expression associated with BRAF mutant-like CRC to find predictive markers and acquired gene alterations to detect resistance mechanisms to eribulin. We initiated patient enrolment in March 2018, completed the primary analysis on May 2019, and are currently continuing with the liquid biopsy part., Trial Registration Number: UMIN000031221 and 000031552., Competing Interests: Competing interests: TM has received honoraria from Takeda, Chugai, Merck Serono, Taiho, Bayer, Lilly Japan, Yakult Honsha, and Sanofi and has received research funding from Yakult Honsha, MSD, Daiichi Sankyo, and Ono; HT has received honoraria from Takeda, Chugai, Merck Serono, Taiho, Bayer, Lilly Japan, and Yakult Honsha, Sanofi; DK has received honoraria from Takeda, Chugai, Lilly and Merck Serono; HB has received honoraria from Taiho and Eli Lilly Japan and has received research funding from Taiho, Astrazeneca and Sysmex; YK has received honoraria Takeda, Chugai, Bristol-Myers Squibb, Ono, Merck Biopharma, Taiho, Bayer, Lilly, Yakult Honsha, Sanofi, Nipro, Moroo, Asahi Kasei, Mitsubishi Tanabe, Otsuka, Medical Review, and Shiseido and has received research funding from MSD, Daiichi Sankyo, NanoCarrier, Eisai, Sysmex, Shionogi, IQVIA, Parexel International, Astellas, Mediscience, Sumitomo Dainippon, A2 Healthcare, Ono, Taiho, Bayer, Yakult Honsha, and Sanofi, ES has received honoraria from Taiho, Yakult, Chugai, Lilly, Sanofi, Merck bioparm, and Takeda; TEN has received honoraria from Takeda, Chugai, Merck Serono, Taiho, Bayer, Lilly Japan, Sanofi, Kyowa Hakko Kirin, Sawai, Bristol-Myers Squibb Japan, Ono, Dainippon Sumitomo Pharma, MSD, Nippon Kayaku, Celltrion Healthcare Japan, and Teijin and has received research funding from Takeda, Chugai, Merck Serono, Taiho, Lilly Japan, Sanofi, Ono, Dainippon Sumitomo Pharma, MSD, Nippon Kayaku, Eisai, Daiichi Sankyo, A2 Healthcare and Solasia Pharma; TS has received honoraria from Chugai, Merck Serono, Bristol-Myers Squibb, Takeda, Yakult Honsha, Lilly, Bayer Yakuhin, Ono, Merck, Astellas Pharma, Taiho and Nihonkayaku, has received consulting or advisory role from Bayer, Lilly, Ono, Takara Bio, Merck Serono, and Nihonkayaku, and has received research funding from Yakult Honsha, Chugai, Ono, Sanofi, Lilly, Daiichi Sankyo, Merck Serono, Gilead Sciences, and Dainippon Sumitomo; TE has received honoraria from Lilly, Taiho, Bristol-Myers Squibb Japan, Eisai, Daiichi Sankyo, Merck Serono, Chugai, Ono, Takeda, Bayer, and Sanofi and has received research funding from Daiichi Sankyo, Merck Serono, MSD, Novartis, Dainippon Sumitomo, Ono, Astellas Pharma, Lilly, Bayer, Nihonkayaku, Pfizer, and Bristol-Myers Squibb Japan; MW has received honoraria from Chugai and Johnson and Johnson; SN has received honoraria from Taiho and Astrazeneca, AS has received research funding from MSD, Eisai, Ono, Taiho, Takeda, and Bayer, Atsushi Ohtsu has received honoraria from Ono, BMS, Chugai, Taiho, Eisai, and Amgen and has received research funding from Bristol-Myers Squibb and immediate family member of Atsushi Ohtsu have been employed by Celgene, and Takayuki Yoshino has received research funding from Novartis, MSD, Sumitomo Dainippon, Chugai, Sanofi, Daiichi Sankyo, Parexel, Ono, GlaxoSmithKline and Boehringer Ingelheim., (© Author (s) (or their employer(s)) 2019. Re-use permitted under CC BY-NC. No commercial re-use. Published by BMJ on behalf of the European Society for Medical Oncology.)