Genomic analysis of primary epithelial neoplasms of the seminal vesicle identifies a subset of mucinous cystic tumours driven by KRAS mutations

Background Carcinomas of the seminal vesicle are exceedingly rare, with a limited number of cases described in the literature. Reported cases span a relatively wide morphological spectrum, and their genomic features remain unexplored. Design In this study, we interrogated five primary epithelial neoplasms of the seminal vesicle using a targeted DNA sequencing platform (OncoPanel, 447 genes). Results The tumours included one adenocarcinoma with intestinal phenotype presenting after external beam radiation (for prostatic adenocarcinoma), one carcinoma with Müllerian‐type clear cell phenotype, two mucinous tumours resembling low‐grade mucinous neoplasms of the appendix (LAMN) and one mucinous cystadenoma. The post‐radiation mucinous adenocarcinoma had genomic findings consistent with bi‐allelic inactivation of TP53 , as well as multiple copy‐number changes with regional and chromosomal arm‐level copy‐number losses. The Müllerian‐type clear cell carcinoma exhibited a complex copy‐number profile with numerous regional and arm‐level copy‐number changes, as well as focal amplification events, including copy‐number gain of 8q and amplification of a region within 20q13. Both low‐grade mucinous tumours resembling LAMN harboured hot‐spot gain‐of‐function KRAS variants (p.G12V and p.G13D) as the only genomic alteration. No genomic alterations were detected inthe lesion diagnosed as mucinous cystadenoma. Conclusion Our results suggest that primary low‐grade mucinous neoplasms of the seminal vesicle may represent a distinct entity equivalent to appendiceal counterparts, driven by gain‐of‐function variants of RAS GTPases. The remaining tumours showed genomic features that closely resembled those of neoplasms with comparable phenotypes and/or biological characteristics arising in other sites, suggesting that they could be managed similarly, with special considerations related to their anatomical location.