Amebiasis is an infectious disease caused by oral ingestion of cysts of the protozoan parasite . This disease is classified into extraintestinal amebiasis and intestinal amebiasis (amebic colitis) . Amebic colitis is a diarrheal disease, but is rarely predicted as an adverse event during cancer treatment because Japan is not considered to be an endemic country. We report a case of amebic colitis in a 60-yearold man who developed diarrhea during chemoradiotherapy for oropharyngeal cancer. Initially, we considered that he had cytotoxic agent-related intestinal mucositis or an enteral feeding-related diarrhea.However, treatments such as bowel rest and administration of antibiotics did not result in improvement.We conducted further examinations to investigate the cause of the intractable diarrhea. Computed tomography showed inflammation of the entire colon, and a colonoscopy enabled a correct diagnosis to be made. Only conservative management, which comprised administration of metronidazole and paromomycin, rapidly improved his symptoms. Finally, the patient was able to achieve the planned cancer treatment.Amebiasis is an infectious disease in Japan that requires a thorough survey to be conducted for its diagnosis. The number of cases of amebiasis rapidly increased after 2000, and there are more than 10,000 asymptomatic carriers. Furthermore, the route of infection was not identified in approximately half of the cases reported in the past 5 years. The disease can result in manifestations, such as liver abscess, brain abscess and intestinal perforation, and death may occur if the diagnosis of amebiasis is delayed. Therefore, even if there is no obvious risk of infection but diarrhea is more severe than usual during chemotherapy, physicians should consider the possibility that patients may be infected with this disease. Prompt collaboration with a gastroenterologist for a detailed examination should then be carried out.
