Atypical squamous cells in urine cytology are associated with a significant risk of high-grade malignancy

Atypical squamous cells (ASC) in urine cytology are rarely found, and their clinical significance is not well studied. Previous studies were limited by a small number of cases and a lack of objective grading of ASC and/or their correlation with accompanying urothelial cell abnormality (UCA).

The institutional database was searched over 10 years for urine cytology reports containing ASC or from patients who had a concurrent diagnoses of high-grade (HG) urothelial carcinoma with squamous differentiation or squamous carcinoma. ASC were defined as keratinized squamous cells and were subcategorized as reactive, koilocytosis, low-grade (LG) atypia, and HG atypia. Correlations with age, sex, specimen type, accompanying UCA, number of ASC, and the risk of HG malignancy (ROHM) were assessed.

ASC were present in 0.15% of all urine specimens (123 of 81,018). Slides and clinical follow-up were available on 91 patients (median age, 71 years). LG and HG squamous atypia had ROHMs of 70% and 92%, respectively. ASC not accompanied and accompanied by UCA had ROHMs of 37% and 94%, respectively. Most malignancies (34 of 67; 51%) showed rare ASC in urine. Reactive changes and koilocytosis had 0% ROHM.

ASC in urine cytology is a significant finding and is associated with a high ROHM. In the absence of accompanying UCA, LG squamous atypia had a lower ROHM than HG atypia. In the presence of UCA, LG and HG squamous atypia had ROHMs of over 90%. These findings suggest that ASC and their grade of atypia should be noted in the cytology report, and clinicians should be made aware of their clinical significance.