[A case of rectal submucosal tumor diagnosed with the coexistence of gastrointestinal neuroendocrine tumor G1 and adenocarcinoma following endoscopic submucosal dissection].

In a 67-year-old man, colonoscopy confirmed the presence of a 5-6mm submucosal tumor in the upper rectum (Ra);the tumor showed a tendency to grow with the size appearing to be 9-10mm at re-examination that was performed 1 year thereafter. No findings on computed tomography indicated metastasis. A neuroendocrine tumor (NET) was suspected, and endoscopic submucosal dissection was performed. The patient was pathologically diagnosed with coexistence of NETG1 and a well-differentiated adenocarcinoma. Few reports have described the coexistence of relatively low-grade NETG1 and an adenocarcinoma in the Ra, and such an occurrence is considered rare. The patient has shown no recurrence at 3 years and 2 months postoperatively.