ABSTRACT
Upper tract urothelial carcinoma (UTUC) presents diagnostic challenges due to small biopsy specimen size, poor orientation, and technical obstacles that can yield equivocal diagnoses. This uncertainty often mandates repeated biopsies to evaluate the necessity of nephroureterectomy. Prior studies have suggested cytokeratin 17 (CK17) immunostain as an adjunctive tool for diagnosing bladder urothelial neoplasia in both urine cytology and tissue biopsy specimens. We evaluated the utility of CK17 in differentiating UTUC from benign urothelium and its ability to stratify low-grade from high-grade neoplasia. Our study involved a cohort of previously diagnosed cytology (n = 29) and tissue specimens from biopsies and resections (n = 85). We evaluated CK17 staining percentage in cytology and tissue samples and localization patterns in biopsy/resection samples. Our findings showed a statistically significant distinction (p < 0.05) between UTUC and benign tissue specimens based on full thickness localization pattern (odds ratio 8.8 [95% CI 1.53-67.4]). The percentage of CK17 staining failed to significantly differentiate neoplastic from non-neoplastic cases in cytology or tissue samples. Additionally, based on prior research showing the efficacy of CK20/CD44/p53 triple panel in bladder urothelial neoplasia, we utilized tissue microarrays to evaluate if these markers could distinguish UTUC from benign urothelium. We found that CK20/CD44/p53, individually or in combination, could not distinguish urothelial neoplasia from non-neoplasia. Full thickness CK17 urothelial localization by immunohistochemistry was highly reproducible with excellent interobserver agreement and may play a supplementary role in distinguishing upper tract urothelial neoplasia from benign urothelium.