Cytological Appearances of Colorectal Adenocarcinoma Cells in Urine

The Paris System for Reporting Urinary Cytology (TPS) has clearly and simply identified the criteria for the accurate diagnosis of high-grade urothelial carcinoma (HGUC); however, the urine cytological findings of secondary tumours have not been fully assessed. Therefore, we evaluated the urine cytological features of colorectal adenocarcinoma cells that invaded the urinary tract.

Thirty urine cytology specimens with cells considered colorectal adenocarcinoma were retrieved by clinicopathological review, subject to the following criteria: no urothelial carcinoma history, diagnosed as HGUC by TPS and supported by CDX-2 immunocytochemistry. Cases were morphologically re-evaluated.

CDX-2 immunostaining, performed in four available cases, showed nuclear positivity in all cases. Tall columnar carcinoma cells were identified in 12/30 cases, tumour cells with pale or vacuolated cytoplasm in 4/30, large and eosinophilic nucleoli in most atypical cells in 4/30, large cells simulating HGUC cells in 27/30 and small cells with irregularly shaped or crescentic nuclei in 27/30. A histological review of transurethral or colorectal resection specimens revealed morphologically identical small cells on the surface of all well-to-moderately differentiated adenocarcinomas, demonstrating desquamated and degenerated adenocarcinoma cells. One cytological specimen from a poorly differentiated adenocarcinoma showed dispersed isolated tumour cells with uniform and round nuclei containing finely granular chromatin and prominent nucleoli.

Colorectal adenocarcinoma cells in the urine may not only be large and tall columnar or vacuolated, but can also simulate HGUC cells or have small round or crescentic nuclei. Recognising this morphological diversity is important for accurate diagnosis.