P25-5 Effective Treatment of Chemotherapy with EGFR Ab for an Unresectable Lynch Syndrome-Associated Small Intestinal Cancer

Lynch syndrome is a hereditary disease caused by germline variants of the MMR gene, which impairs the MMR mechanism and results in MSI, leading to canceration. In recent years, it has been reported that ICI is effective for cancers in which the MMR mechanism is impaired, but there are few reports showing the effectiveness of cytotoxic and molecular-targeted agents. The case was 67-year-old man who was being followed up after surgery for colorectal cancer, and was diagnosed with a small intestine tumor with distant lymph node metastasis by CT and PET in August 2017. Laparoscopic partial resection of the small intestine + mesenteric lymph node biopsy were performed. The pathological result was a diagnosis of primary small intestine cancer and its lymph node metastasis. When chemotherapy with anti-EGFR antibody was started for mesentery and distant lymph node metastasis, the area shrank, leading to CR. Screening for Lynch syndrome revealed a pathogenic variant in the germline, which was diagnosed as Lynch syndrome. Chemotherapy was continued and CR was maintained, but treatment was discontinued in December 2018 due to patient reasons. Thereafter systemic chemotherapy was started with a diagnosis of bladder cancer in February 2019, but it was refractory to treatment. Pembrolizumab therapy was started in July of the same year, but bladder cancer increased and metastatic bone tumors were presented. In February 2020, the patient moved to home care. At that time, mesenteric and distant lymph node metastasis derived from small intestine cancer remained CR. We report a case of unresectable Lynch syndrome-related small intestine cancer in which anti-EGFR antibody-combined chemotherapy was effective, with a review of the literature.