- Design
- Retrospective morphological, immunohistochemical and molecular study
- Population
- 37 en bloc resection specimens from 25 patients with high-grade papillary urothelial carcinoma
- Primary outcome
- Extent, clonality and immunoprofile of lateral extension
- Effect
- Mean length 4.7 mm (1.5–10.8); margin reached in 12/13; clonal in 9/11
A US group reviewed 37 en bloc transurethral resection specimens from 25 patients with high-grade papillary urothelial carcinoma, looking at the flat atypical urothelium that sometimes spreads sideways from the base of the papillary tumour.
Lateral extension was present in 13 tumours, averaging 4.7 mm and reaching up to 10.8 mm. It ran to the mucosal margin in 12 of 13 (92%). In 9 of 11 sequenced pairs it shared pathogenic alterations with the papillary tumour, supporting a common origin. All showed abnormal CK20 staining and 3 of 11 aberrant p53 — patterns usually read as carcinoma in situ.
Two practical points follow. Lateral extension can be reported as carcinoma in situ when it is part of the papillary lesion, which may overstate risk. And it often reaches the margin, so the extent of resection matters if the aim is complete removal. The series is small and needs outcome data before it changes grading rules.
- Look for flat atypical urothelium contiguous with the base of a papillary tumour before calling separate carcinoma in situ
- Comment on lateral extension and its relation to the mucosal margin in en bloc specimens
- Interpret CK20 and p53 in context — both can mimic carcinoma in situ here
- Discuss reporting conventions with urologists so lateral extension is not over-treated
Why it matters
Calling lateral extension carcinoma in situ can escalate treatment for a patient whose disease is a single papillary lesion.
Don't overread it
A small descriptive series without outcome data; it does not yet establish how lateral extension affects recurrence.
The statistics, in plain English
The numbers are small: 13 tumours with lateral extension and 11 sequenced. The 92% margin involvement is striking but comes from 12 of 13 cases, so the true figure could be lower.
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