Metastatic Mixed Adeno-Neuroendocrine Carcinoma of the Colon to the Liver with Multiple Peritoneal Deposits: A Case Report.

BACKGROUND Metastatic mixed adeno-neuroendocrine carcinoma (MANEC) is a rare malignancy. It is characterized by the presence of both neuroendocrine and epithelial components, each of which constitute at least 30% of the lesion to establish the diagnosis. CASE REPORT A 48-year-old man presented with a 1-month history of right upper-quadrant pain and unintentional weight loss of 18 kg. He was also complaining of constipation and fatigue for 6 days. The initial diagnosis from a referring hospital was colon cancer with liver metastasis based on a computed tomography (CT) scan of the chest, abdomen and pelvis. After re-evaluation at our hospital, the scan revealed multiple peritoneal deposits in addition to the previously reported findings. A colonoscopy and biopsy were performed, after which the histopathological examination demonstrated a mixed poorly differentiated large cell neuroendocrine carcinoma and adenocarcinoma. Based on the imaging and histopathology reports, he was diagnosed with a poorly differentiated MANEC of the colon with liver metastasis and multiple peritoneal deposits. His lesions were deemed unresectable, and he was referred to the oncology department for palliative care. There he received a total of 9 cycles of cisplatin and etoposide for 8 months. His CT scan showed a regression of the primary tumor indicating a good response to chemotherapy. The patient is still following up with his medical oncologist. CONCLUSIONS Although it is rare, MANEC is a complex neoplasm that requires a high index of suspicion to diagnose due to its nonspecific presentation. It is confirmed through histopathology and immunohistochemistry of the tumor biopsy. Imaging is performed for staging, with most patients presenting at advanced stages with metastases. The only curative option is complete surgical resection of both the primary and metastatic lesion. Many cases, however, are regarded as unresectable and are referred for palliative treatment.