Novelty: Malignant peritoneal mesothelioma (MPM) is a rare disease confined to peritoneal cavities in most cases, seldom seen in intraand extra-abdominal invasion. In addition, MPM is easy of misdiagnosis and has a poor prognosis. Here, we report a case of colonic invasion induced by MPM in order to help prevent from misdiagnosis and prolong survival time. A 53-year-old male who presented with constipation, weight loss, and occasional abdominal discomfort for 2 months was admitted to the Department of Surgical Oncology, Harbin Medical University Cancer Hospital, November 2013. He was a heavy smoker of 15 packs/month with a history of asbestos exposure in childhood and diabetes mellitus. On physical examination, he had a fixed mass in the right lower quadrant. Routine blood tests and evaluation for tumor markers CEA, CA724, CA19-9, and CA-125 were all in normal range except for a thrombocytosis of 397×10/L. A 3D-enhanced CT of the abdomen showed an irregular thickening wall of hepatic flexure of colon, and the thickener area can be reached 16.8 mm, closely adjacent to intestine. At the same time, an infiltrating mass of 67.7 mm in size, multiple small peritoneal nodules, and abdominal swelling lymph nodes can also be seen in abdominal CT. There were no remarkable findings on the endoscopic examination, and the colonoscopy suggested an infiltrating lesion located in the hepatic flexure of colon, ruptured in the surface, and easily bled when touched. Laparotomy was performed, peritoneal nodules were intraoperatively found throughout the peritoneum, and the infiltrating mass had penetrated the range of serosal and right side of the peritoneum, widely planting in the peritoneum, omentum, and surface of peritoneal cavities. Necrotic tissue sample was delivered for examination, and quick pathology revealed malignancy. In addition, 2.0 cm×1.5 cm×1.0 cm omental tissue was cut for detection during surgery. Histology revealed a well-differentiated epithelioid malignant mesothelioma. It was positive for HBME-1, CK5/6, CK7, and calretinin, supporting the diagnosis of MPM. After surgery, the patient was referred to the Department of Medical Oncology. Our patient recovered well after the operation, and he had successfully accepted 2 cycles of chemotherapy of pemetrexed combined with carboplatin; unfortunately, he did not tolerate the therapy, and the disease progressed with the appearance of ascites and rectum occupation revealed by abdominal and pelvic CT. However, there are no significant abnormalities found in colonoscopy. We deemed that rectum occupation was caused by the compression of swelling lymph nodes. Oxaliplatin and capecitabine were adjusted to the following treatment, and he felt symptoms released at present. MPM is an uncommon, fatal disease arising from the peritoneum with an increasing incidence of 7–40/million and a negative prognosis of within 12 months [1]. The main risk factor for MPM is asbestos exposure, and the onset of about 60 % of MPM patients was correlated with direct or indirect asbestos contact. In addition, exposure to radiation, talc, mica, erionite, Thorotrast, SV40, and Hodgkin’s disease has also been reported to be related to MPM [2]. The most common presentations of MPM are abdominal pain and distension which resulted from the accumulation of tumors and ascites, while constipation is exceptional. MPM is usually diagnosed at advanced stage due to its nonspecific clinical and S. B. Cao and S. Jin contributed equally to this work. S. B. Cao : S. Jin : J. Y. Cao : J. Shen : J. W. Zhang :Y. Yu (*) Department of Medical Oncology, Harbin Medical University Cancer Hospital, No. 150 Hapin Road, 150081 Harbin, China e-mail: yuyan_hrb@126.com