Pitfalls of frozen section diagnosis in ureter margin evaluation of plasmacytoid urothelial carcinoma of urinary bladder.

Background: Plasmacytoid urothelial carcinoma (PUC) is a rare and aggressive subtype that often presents at advanced stages with poor prognosis. This study investigated tumor invasion to better understand tumor behavior and potentially to improve management strategies by comparing the clinicopathologic characteristics of PUC with positive ureter resection margin (+ URM) with PUC with negative URMs (-URM).

Methods: This retrospective analysis used pathology reports from 2017 to 2023 for cases diagnosed with PUC during radical cystectomy (RC). All applicable H&E slides of RC specimens were reviewed. Cases with a plasmacytoid component greater than 25% in the RC specimens were analyzed. Frozen section analyses (FSAs) and permanent section analyses (PSAs) of ureter resection margins were performed.

Results: Fifteen patients with a plasmacytoid component greater than 25% in their RC specimens were identified. Compared with -URM PUC cases, +URM PUC cases were located more frequently at the trigone or bladder neck, and all + URM cases exhibited ureter orifice involvement. Among 6 PSA-positive cases, three (50%) cases showed discrepancies with FSA. Three + URM cases exhibited PUC tumor cells along the submucosa and muscularis propria layer, and the 3 remaining cases showed PUC tumor cells along the adventitia. We observed a consistent adventitia invasion in all the discordant cases, with sectioning errors and misinterpretation identified as the primary causal factors.

Conclusion: To the best of our knowledge, this is the first study to demonstrate two separate patterns of tumor infiltration along the ureter and to discuss the significance of comparing FSA with PSA in PUC. The significance of comprehensive management strategies for PUC patients, including a thorough evaluation of ureteral margins and accurate interpretation of periureteral fat tissue, is highlighted. Large, well-designed studies are needed to strengthen the evidence and to establish optimal management strategies for patients with PUC.