[Difficult diagnoses of two cases of double cancer involving malignant lymphoma with peritoneal localization and malignant abdominal tumor].

We encountered two cases of malignant lymphoma with peritoneal localization complicated by sigmoid colon cancer and hepatocellular carcinoma. Multiple primary cancers were suspected on the basis of differences in absorption values on computed tomography (CT) and differences in the degree of accumulation on positron emission tomography CT; however, a definitive diagnosis based on these findings alone was difficult. Endoscopic ultrasound-guided fine-needle aspiration was useful for determining the diagnosis and treatment strategy. In cases of double cancers involving malignant lymphoma with peritoneal localization and malignant abdominal tumor, differentiation and staging are often difficult, which increases the risk of selecting the wrong treatment strategy. Therefore, care must be taken when diagnosing these diseases.