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

BACKGROUND: 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).

METHODS: 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.

RESULTS: 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 accompanied and not 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.

CONCLUSIONS: 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.