Clinicopathological significance of TUBB3 in upper tract urothelial carcinoma and possible application in urine cytology

βIII‐Tubulin, encoded by the TUBB3 gene, is a microtubule protein. We previously reported that TUBB3 is overexpressed in renal cell carcinoma. We investigated the clinicopathological significance of TUBB3 in upper tract urothelial carcinoma (UTUC) by immunohistochemistry. In normal tissue, TUBB3 expression was weak or absent. In contrast, TUBB3 overexpression was observed in urothelial carcinoma (UC) tissues in 51 (49%) of 103 UTUC cases. TUBB3 overexpression was associated with nodular/flat morphology, high‐grade disease, high T stage, and a poor prognosis. Similar results were obtained in The Cancer Genome Atlas bladder cancer cohort. TUBB3 expression was also associated with high Ki‐67 labeling index, CD44v9, HER2, EGFR, and p53 expression in UTUC. Among representative cancer‐related molecules, TUBB3 was an independent predictor of progression‐free survival and high‐grade UC. Finally, using urine cytology samples, we analyzed TUBB3 expression by immunocytochemistry. TUBB3 expression was more frequently found in UC cells than in nonneoplastic cells. The diagnostic accuracy of urine cytology was improved when combined with TUBB3 immunostaining. The findings suggest the importance of TUBB3 in tumor progression and its potential application as a biomarker for high‐grade disease and the prognosis of UC. Moreover, combination with TUBB3 immunostaining might improve the diagnostic accuracy of urine cytology.