[Clinicopathological features of colorectal amphicrine carcinoma]

Objective: To investigate the clinicopathological, immunophenotypic and molecular features of colorectal amphicrine carcinoma (AC). Methods: Eight cases of colorectal AC were collected at the Nanjing Drum Tower Hospital and Nanjing First Hospital, Nanjing, China from 2013 to 2020. The histopathological, immunohistochemical and molecular features were analyzed. The relevant literature was reviewed. Results: There were 6 males and 2 females, with an average age of 56 years (range 28-80 years). The tumor sites were as follows: 4 cases in sigmoid colon, 3 cases in rectum, and 1 case in transverse colon. Microscopically, there were three different patterns in the tumors, including nests with collagen hyperplasia, sheets of cells with scant stroma, and glandular or cribriform growth of goblet- or signet ring-like cells. The tumor cells generally had abundant cytoplasm with abundant mucin or eosinophilic granules. The nuclei were oval or irregular with fine chromatin and inconspicuous nucleoli. Mitotic figures were common. Neuroendocrine granules and mucin granules could be identified clearly under electron microscope. All cases showed frequent perineural and lymphovascular invasions, lymphatic metastasis, and advanced stage. Regarding immunohistochemical and specific stains, the tumor cells expressed more than two neuroendocrine markers, particularly CD56 and synaptophysin which were diffusely positive in 7 of the 8 cases. They also showed intracellular mucin in the amphicrine components which was positive for D-PAS. KRAS G12C or NRAS Q61 gene mutations were found in 2 patients. Among the six cases with complete follow-up, four of them died of the disease within three years of the diagnoses, while two were alive without known disease progression. Conclusions: Colorectal AC is a rare, distinct entity with both epithelial and neuroendocrine differentiation. It mainly occurs in the sigmoid colon and rectum. It typically has aggressive clinical courses, dismal prognosis and characteristic histological features and immunophenotype, which highlight the importance of recognizing this entity for clinicians and pathologists.