An institutional experience with The Paris System: A paradigm shift from ambiguous terminology to more objective criteria for reporting urine cytology

Background Urine cytology is a highly specific modality for diagnosing high-grade urothelial carcinoma (HGUC), but plagued by low sensitivity and wide inter-observer variability mainly ascribed to the lack of an established template of reporting. The Paris System (TPS) working group proposed such a template at the 2013 International Congress of Cytology, replete with objective criteria for categorising specimens into one of the seven categories: non-diagnostic, negative for HGUC, atypical urothelial cells, suspicious for HGUC, HGUC, low-grade urothelial neoplasm and others (including non-malignant entities). This study was undertaken to determine the impact of TPS criteria in the morphological interpretation of urine samples. Methods A total of 255 voided urine specimens from 97 patients who had follow-up biopsies were re-assessed according to TPS criteria and correlated with the final histological diagnosis. Results Sixty-three patients were diagnosed with HGUC, and 34 had low-grade papillary UC on biopsy. Earlier samples from 40 (41.2%) patients were categorised as merely “atypical” wheereas the “positive for malignancy” category was assigned to 33 (34%) patients. After re-evaluation of the same cases using TPS criteria, cytological features in 44 (69.8%) out of 63 HGUC patients were correctly recognised as HGUC and samples from additional seven patients were re-categorised as suspicious for HGUC (total 81%). The sensitivity of the HGUC category in predicting HGUC was 69.8% which rose to 81% when HGUC was grouped with suspicious for HGUC category. Conclusion The criteria outlined by TPS facilitated the standardisation of urine cytology reporting and significantly increased the sensitivity of diagnosing HGUC.