Urachal carcinoma: from gross specimen to morphologic, immunohistochemical, and molecular analysis.

Urachal carcinoma (UrC) is an exceedingly rare neoplasm that develops from the urachus, an embryologic remnant of the urogenital sinus and allantois. The most commonly encountered histologic subtype is adenocarcinoma. The aim of this study is to characterize a series of UrC by morphology, immunohistochemistry, and molecular analysis. We retrospectively investigated seven cases of UrCs and assessed patient symptoms, imaging, histologic features, immunohistochemical profile, molecular characteristics, pathologic stages, and type of treatment. Immunostaining for CK7, CK20, Muc-2, CDX2, GATA3, β-catenin, and CK34βE12 was carried out on each neoplasm and on seven non-neoplastic urachal remnants as the control group. Additionally, a mutational analysis was performed using the QIAact Actionable Insights Tumor Panel Kit, which analyzes KRAS, NRAS, KIT, BRAF, PDGFRA, ALK, EGFR, ERBB2, PIK3CA, ERBB3, ESR1, and RAF1. Our cohort comprised five females and two males with a mean age of 64 years. UrCs consisted of two mucinous cystadenocarcinomas and five invasive, non-cystic adenocarcinomas. Carcinoma antigen expression profile was positive for CK20 and negative for CK34βE12 and GATA3 in all cases. Five of seven cases stained positively for Muc-2 and CDX2. On the contrary, non-neoplastic urachal remnants were immunoreactive for CK34βE12, CK7, and GATA3. Mutational analysis gave a positive result in four out of seven (57.1%) cases. All four positive tumors showed RAS mutation and one an additional mutation in PIK3CA. Urachal tumors exhibit peculiar morphologic, immunohistochemical, and molecular features. Due to the advanced stage at presentation, individualized treatment should be undertaken.