Clinicopathological and molecular characterization of extra-appendix goblet cell adenocarcinomas.

Goblet cell adenocarcinoma (GCA) is a distinctive type of endocrine-exocrine mixed tumor, exhibiting intermediate morphological features between neuroendocrine tumor and adenocarcinoma. It predominantly arises in the appendix, but primary extra-appendiceal GCA is extremely rare. Here, we presented six cases of primary extra-appendiceal GCA from 2016 to 2022. Notably, one case was originating in the bladder which was the first report of primary GCA to occur outside the digestive tract. The tumors frequently displayed variable goblet cell morphology, characterized by cytoplasmic mucin accumulation and basally located nucleus. Low-grade components typically exhibited glandular or clustered patterns without prominent fibrotic responses. High-grade components demonstrated cribriform, cluster and single-file arrangement accompanied by marked fibrous reactions. Immunohistochemically, the tumors showed positivity for both neuroendocrine markers（synaptophysin, chromogranin A, CD56 ）and adenoids markers（CDX-2, CK20）. Next-generation sequencing revealed the most prevalent mutated genes within GCAs were TP53. Due to their morphological and immunohistochemical similarities to primary appendiceal GCA counterparts, we propose a distinct category for extra-appendiceal Goblet cell adenocarcinoma.