Clinicopathological characteristics of co-existing or mixed colorectal cancer and neuroendocrine tumor: Report of five cases

Coexisting or mixed type of colorectal tumors has been rarely reported. This study was designed to investigate clinicopathological characteristics of co-existing or mixed colorectal adenocarcinoma and highly differentiated neuroendocrine tumor (NET-G1). To do that, clinicopathological characteristics of five cases of co-existing or mixed colorectal adenocarcinoma and NET-G1 admitted to our institution between 2017 and 2021 were retrospectively analyzed and literature review was conducted. Four patients were male and one female, aged 62-75 years old. Among them, four cases were diagnosed with rectal cancer and one case of colon cancer. Gross examination found that one patient was diagnosed with multiple colon polyps including three malignant polyps, and the remaining four cases of ulcerous masses. The tumors infiltrated into the muscle layer in two cases, and three cases with tumors infiltrating into surrounding adipose tissues. Microscopic examination revealed one patient developed poorly differentiated adenocarcinoma and four cases of moderately differentiated adenocarcinoma. Four patients had adenocarcinoma and NET-G1 in colon, and one case of adenocarcinoma in colon and NET-G1 in appendix. To conclude, co-existing or mixed colorectal tumors are extremely rare in clinical settings. Clinicopathological characteristics of five cases of co-existing or mixed adenocarcinoma and NET-G1 are diverse and adenocarcinoma is more aggressive in most affected patients.