Nuclear hypochromasia: Shedding light on the "lightness" of high-grade urothelial carcinoma.

Background: The Paris system (TPS) has provided a standardized classification for reporting urinary cytology, specifically high-grade urothelial carcinoma (HGUC). While hyperchromasia is well described in HGUC, there exists little data on nuclear hypochromasia in HGUC. Our focus was to investigate the incidence of hypochromasia in HGUC and if it should become a criterion for HGUC.

Design: All cases of HGUC at our institution for a 3-year interval (2017-2019) using TPS were reviewed. Each case had a single ThinPrep slide and concurrent biopsy or resection specimen to confirm the diagnosis within 30 days. The presence of hypochromasia was evaluated, and cases with hypochromasia were stratified based on the tumor cell percentage. Cases with hypochromasia in 5% or greater of the tumor cells were considered "positively identified" for hypochromasia.

Results: We reviewed 117 cases of HGUC and identified nuclear hypochromasia in 12 cases (10.2%) within 5% or greater of the tumor cells. These 12 cases were further assessed based on if tumor cells showed hypochromasia in 5%-49% of the sample, or greater than 50% of the sample. Hypochromasia in 5%-49% of tumor cells was present in 8/117 cases (6.8%); whereas in 50% or greater samples 4/117 cases (3.4%) showed hypochromasia. No cases were identified where hypochromasia was noted in less than 5% of the tumor cells.

Conclusion: TPS and use of hyperchromasia as a feature of HGUC is affirmed. However, hypochromasia, while not diagnostic in isolation, is present in a sub-set of patients with HGUC (10.2%) and should be considered as a variance noted in the nuclei of HGUC.