Urachal cancer-current concepts of a rare cancer.

Urachal cancer is a rare but aggressive disease. In addition to the non-glandular tumors, non-cystic urachal adenocarcinomas are nowadays distinguished from the primary cystic variant. (Immunohistochemical) markers are only of minor differential diagnostic value and, therefore, the diagnosis is primarily established in a multidisciplinary approach. The non-cystic variant accounts for the majority of cases (83%), is more common in men (63%), shows a median age at diagnosis of 51 years and has a 5-year survival rate of about 50%. In organ-confined disease, usually a partial cystectomy of the tumor in the bladder dome, including the median umbilical ligament and umbilicus, is performed. In advanced stages, systemic therapy is needed while 5‑fuorouracil (5-FU) containing regimes have been shown to be more effective. Due to the rarity of the tumor, targeted therapy approaches based on a biological rationale are becoming increasingly relevant. As molecular data are still sparse, we compiled and analyzed the largest urachal cancer cohort to date. In 31% of the cases, MAPK-/PI3K signaling pathway alterations were detected (especially in K-/NRAS) with implications for anti-EGFR therapy approaches. Further potentially therapeutic alterations were detected in FGFR1, MET, PDGFRA, and erbB2/HER2. Additionally, PD-L1 tumor cell expression (clone: 22C3) was demonstrated in 16% of cases, therefore making anti-PD-1/PD-L1 immuno-oncological approaches worth considering despite the absence of mismatch repair deficiency (MMR-d) and/or high microsatellite instability (MSI-h). Finally, urachal adenocarcinomas seem to be a distinct entity on the molecular level with closer resemblance to colorectal adenocarcinomas than to urothelial carcinomas.