Non-invasive papillary urothelial carcinoma with 'micropapillary' architecture: clinicopathological study of 18 patients emphasising clinical outcomes.

Abstract

Invasive micropapillary carcinoma is a recognised aggressive urothelial carcinoma variant. One prior study focusing on non-invasive (pTa) high-grade papillary urothelial carcinoma with micropapillary architecture has been reported. We collected bladder transurethral resection specimens showing non-invasive high-grade papillary urothelial carcinoma with non-hierarchical secondary papillae lacking fibrovascular cores (i.e. micropapillary architecture). Cases with any invasive component or any prior history of invasive urothelial carcinoma were excluded. Twenty cases were identified from 16 male and two female patients (aged 55-86years). Micropapillary architecture comprised from 10 to 95% (mean=31%), but non-invasive cribriform (15 cases, comprising 5-60%, mean=19%) and villoglandular patterns (nine cases, comprising 5-60%, mean=24%) were commonly admixed. Treatment data were available for 16 patients: surveillance (n=13), cystoprostatectomy (n=1), BCG plus mitomycin (n=1) and BCG (n=1). Follow-up data were available from 16 patients (range=1-128months, mean=50months): 13patients had no new occurrences to date (81%), two had stage progression to pT1 papillary urothelial carcinoma (13%) with one dying of other causes, and one died of other causes with no evidence of disease (6%). Non-invasive urothelial carcinomas with micropapillary architecture are often admixed with non-invasive cribriform and villoglandular patterns. Stage progression to lamina propria invasion in only two of 16 patients (13%) is not higher than expected for otherwise typical pTa high-grade urothelial carcinomas and no progression to invasive micropapillary carcinoma was identified, adding further support to the current World Health Organisation recommendation excluding use of the term 'micropapillary' for pTa urothelial carcinoma.