Are we on track for diagnosing high‐grade urothelial carcinoma with a minimum quantity of five malignant cells in lower tract specimens? Critical analysis of The Paris System Quantitation Criteria

Background The Paris System for Reporting Urinary Cytology (TPS) has gained universal acceptance as the standard for reporting urine cytology requiring at least 5–10 malignant cells to diagnose high‐grade urothelial carcinoma (HGUC) in lower and upper urinary tract specimens, respectively. These quantitation criteria are still subject to discussion, and this study specifically aims to validate the quantitation criterion of HGUC in lower urinary tract. Design The authors reviewed two cohorts of lower urinary tract cases. The first cohort consisted of 100 liquid‐based ThinPrep slides with the diagnosis of HGUC having positive histology on concurrent or follow‐up biopsies within 3 months. The second cohort was 36 HGUC cases with negative histology on concurrent biopsies and within 3 months. The number of high‐grade cells (HGCs) meeting the TPS qualitative criteria were counted under the light microscope driven in a grid‐like manner. Results The first 100 urine samples showed five cases (5.0%) with three HGCs, three cases (3.0%) had four HGCs, five cases (5.0%) showed five HGCs, and 25 cases (25.0%) had between 6–10 HGCs. The risk of high‐grade malignancy (ROHM) in cases with five or more HGCs was 100%, whereas those with three HGCs was 60.0%. The second cohort of HGUC was considered “positive” despite a negative histology. Conclusion This study confirms that quantitation is an essential key to diagnose HGUC. The current TPS criterion of a minimum of five malignant cells in lower tract is robust with a ROHM of 100%. Diagnosing HGUC with less than five HGCs runs the risk of lowering the ROHM. The Paris System for Reporting Urinary Cytology (TPS) requires at least 5–10 malignant cells to diagnose HGUC in lower and upper urinary tract specimens, respectively, which is still subject to discussion due to lack of sufficient data validating the numbers. We retrospectively study 2 cohorts of urine specimens with diagnosis of HGUC, specifically aimed at validating the quantitation criterion. First cohort consisted of 100 liquid‐based slides with the diagnosis of HGUC having positive histology and second cohort was 36 HGUC cases with negative histology, both on concurrent or follow‐up biopsies within 3 months. The number of HGCs meeting the TPS qualitative criteria were counted, and the ROHM calculated. The result showed that the current TPS criterion of a minimum of 5 HGC is robust for the diagnosis of HGUC.