Dysplastic squamous cells are frequently present in urine cytology specimens of patients with high-grade urothelial carcinoma. 
In urothelial carcinoma (UCA), squamous differentiation (SqD) occurs mainly in high-grade UCA with invasion.  Therefore, we sought to determine the frequency of dysplastic squamous cells (DSC) in urine specimens obtained from patients with high-grade UCA asking if DSC could serve as a surrogate marker for high-grade UCA.  We searched for cases with a histologic diagnosis of high-grade UCA and available concurrent cytology, yielding 93 surgical specimens (including 71 biopsies, 12 cystectomies, 5 nephrectomies, 4 ureterectomies, and 1 urethrectomy) from 68 patients with 98 urine cytology samples.  Both cytology and histologic specimens were evaluated for the presence of any SqD on histology and the presence of DSC on cytology besides urothelial cells.  Forty-three of 68 patients (63%) had a cytologic diagnosis of 'positive/suspicious'.  Twenty-one patients (30%) had surgical specimens that showed SqD. Seventeen patients had urine cytology specimens showing DSC (25%).  Thirteen of these 17 patients showed DSC with concurrent malignant urothelial cells, while 4 patients displayed only isolated DSC.  SqD is common in patients with high-grade UCA.  DSC were detected in a subset of specimens from patients with high-grade UCA.  In some instances, isolated DSC on cytology may represent the only evidence of an unsampled high-grade malignancy.