CK20 and p53 Immunohistochemical Staining Patterns in Urinary Bladder Specimens With Equivocal Atypia.

CONTEXT: - Urinary bladder flat carcinoma in situ (CIS) is a worrisome lesion, requiring aggressive surveillance and treatment. Cytokeratin 20 (CK20) and p53 are common immunohistochemical antibodies used to supplement CIS diagnosis in biopsy samples. However, existing data come primarily from unequivocally benign and malignant specimens. OBJECTIVE: - To correlate these markers in specimens with borderline histology with outcomes. DESIGN: - CK20 and p53 immunohistochemistry was analyzed for staining pattern, classified as CIS pattern (both stains yielding strong labeling of the area of concern), discordant (only 1 stain yielding CIS pattern), indeterminate (1 or both stains yielding partial or equivocal labeling), or benign (both stains yielding a benign pattern). RESULTS: - Specimens with equivocal atypia (n = 69) from 65 patients were studied. There were 9 specimens (13%) that had a CIS staining pattern, 18 (26%) were discordant, 31 (45%) were indeterminate, and 11 (16%) were benign. Of the discordant specimens, 13 labeled for CK20 but not p53, whereas 5 showed the opposite. Most specimens (n = 47; 68%) were obtained from patients with a known history of bladder cancer, of which recurrence developed in 27, with an average interval of 37 months (range, 2-216 months). A subset (n = 22; 34%) had no prior history of bladder cancer, from which only 1 patient with CK20-positive/p53-equivocal staining later developed diagnostic carcinoma. CONCLUSIONS: - In our cohort of specimens with equivocal urothelial atypia, very few patients without a prior diagnosis of bladder cancer progressed to diagnostic cancer (1 of 22), suggesting that staining results should be interpreted with caution in de novo atypia. Patients with a known history of bladder cancer had a substantial rate of recurrence, independent of staining pattern.