Abstract
BACKGROUND: With the advancement of medical technology and improvement in living standards, the incidence of multiple primary cancers has gradually increased. In particular, tumors of the digestive system account for a large proportion of multiple primary cancers. The diagnosis and treatment of chronic myeloid leukemia, particularly with synchronous gastric cancer, at the first consultation is relatively rare. CASE SUMMARY: Herein, we present the case of a middle-aged man who was referred to the Department of Hematology owing to an elevated white blood cell count. After the examination, he was diagnosed with chronic myeloid leukemia and was administered imatinib. Three months after the initial diagnosis, he visited our hospital again for abdominal pain, and further examination revealed gastric malignancy. After discussion with a multidisciplinary team, S-1 (Tegafur, Gimeracil, and Oteracil Potassium Capsules) combined with oxaliplatin-SOX regimen-was initiated. Later, the patient's condition rapidly progressed. He developed colonic obstruction and underwent an ostomy; however, he died less than 6 months after the initial diagnosis. CONCLUSION: Multiple primary cancers are influenced by environmental and genetic factors; a standardized multidisciplinary discussion plays a key role in treatment.