Sho Nakamura, Tadahisa Fukui, Shuhei Suzuki, Hiroyuki Takeda, Kaname Watanabe, Takashi Yoshioka Department of Clinical Oncology, Yamagata University Faculty of Medicine, Yamagata, Japan Abstract: Bone marrow metastasis is a rare consequence of colorectal cancer that results in a poor prognosis; few reports describe a favorable response to doublet chemotherapy combined with targeted therapy, which is currently the standard treatment. We experienced a case where anti-epidermal growth factor receptor (EGFR) antibody produced a marked anti-tumor response to bone marrow metastasis that led to long-term survival. A 51-year-old man was diagnosed with a primary KRAS-wildtype rectal cancer with multiple metastases, including the bone marrow. Disease control was achieved for 10.8 months following chemotherapy with a modified FOLFOX6 regimen combined with an anti-EGFR antibody. He died of cancer 22.7 and 16.6 months after disease onset and first-line chemotherapy, respectively. This case shows that early tumor shrinkage and deepness of response to the anti-EGFR antibody were observed even in a patient with bone marrow metastasis. Anti-EGFR antibody therapy should therefore be considered even when a patient’s medical condition appears to be poor owing to bone marrow metastasis. Moreover, tumors that are likely to be sensitive to chemotherapy, such as RAS-wildtype colorectal cancers, can be considered for anti-EGFR antibody therapy even if the patient is considered unfit for chemotherapy. Keywords: colorectal cancer, anti-epidermal growth factor receptor antibody, molecular targeted therapies, disseminated intravascular coagulation, standard of care