Oncologic outcome of mixed adenoneuroendocrine carcinoma (MANEC): A single center case series.

Introduction: Mixed adeno-neuroendocrine carcinomas (MANEC) are rare tumors of gastrointestinal tract mostly found in stomach. There are very few case reports and case series with location of colon and rectum. We aimed to report our results in the treatment of colorectal MANEC.

Methods: We performed a prospective analysis of patients with MANEC diagnosis from December 2011 to March 2019 at National Cancer Institute, Lithuania. The demographic information, tumor details, immunohistochemical markers, clinical data, stage, treatment modalities, clinical and oncological outcomes were collected.

Results: Nine patients with a diagnosis of MANEC were found in our center. The average age at diagnosis was 64.8 (48-91) years. Seven out of nine (77.8%) patients underwent surgery. Distant metastases were observed in five (55.6%) patients. The adenocarcinoma and neuroendocrine tumor as a dominant component were equal in all cases. The most common tumor localizations were sigmoid colon in three patients (33.3%) and rectum - three patients, following two in an anal canal, and one in the hepatic flexure of colon. The adenocarcinoma component was poorly differentiated (G3) in six patients and moderately differentiated (G2) in three patients. The neuroendocrine component was G3 in seven patients (77.8%), G2 - in two patients (22.2%). Median follow-up was 17 months with a median survival time of 12.5 months.

Conclusion: MANEC is very rare, aggressive, rapidly spreading, usually with poor prognosis disease.