Gastrointestinal Amphicrine Carcinoma: A Clinicopathologic Study of Five Patients.

Objective. To investigate the clinicopathological features, immunophenotype, diagnosis, differential diagnosis, and prognosis of amphicrine carcinoma (AC), a rare tumor characterized by dual differentiation between adenocarcinoma and neuroendocrine carcinoma. Methods. The clinicopathological data of five patients with AC diagnosed by pathology at Ningbo Clinical Pathology Diagnosis Center between 2020 and 2024 were collected. These specimens were analyzed using light microscopy, special staining, and immunohistochemical staining. Relevant literature was also reviewed. Results. The study included four men and one woman (range: 21-80 years) with gastric (3) and colorectal neoplasms (2). In all patients, tumor cells exhibited infiltrative growth, involving the subserosal or the serosal layer. Three tumors showed diffuse growth, with some cells displaying signet-ring cell features, others showing poorly differentiated neuroendocrine carcinoma changes, and some cells exhibiting plasmacytoid characteristics. In one patient, tumor cells were arranged in nests, with relatively uniform cell sizes and a palisaded pattern at the periphery. Another patient exhibited most tumor cells arranged in glandular structures with minimal mucin in the cytoplasm. Epithelial markers were positive in all patients. All tumor cells tested positive for AB-PAS staining in the cytoplasm. At least one neuroendocrine marker (synaptophysin, chromogranin A, CD56, insulinoma-associated protein 1) was diffusely and strongly positive in each patient. The expression of mismatch repair proteins (MLH1, MSH2, MSH6, PMS2) and RB protein at immunohistochemistry was retained in all samples. Conclusion. Gastrointestinal amphicrine carcinoma is rare and exhibits distinct histological and immunophenotypic features. The combination of histological morphology, immunophenotype, and AB-PAS special staining is crucial for both the diagnosis and differential diagnosis of this tumor.