- Design
- Retrospective multi-institutional immunohistochemical cohort
- Population
- 88 bladder small cell carcinomas, 79 with immunohistochemistry
- Primary outcome
- Transcription-factor phenotype and expression of therapeutic biomarkers
- Effect
- ASCL1 41.8%, NEUROD1 25.3%, POU2F3 20.3%; NECTIN4 amplification 21.9% (16/73)
A multi-institutional retrospective cohort assembled 88 small cell carcinomas of the bladder, of which 79 were stained for ASCL1, NEUROD1, POU2F3, YAP1 and HNF4 alpha, neuroendocrine markers and several drug targets. Nectin-4 amplification was tested by FISH.
Six immunohistochemical subgroups appeared: ASCL1-driven (41.8%), NEUROD1-driven (25.3%), POU2F3-driven (20.3%), YAP1-driven (6.3%), mixed (5.1%) and negative (1.3%). The first, second and mixed groups were high neuroendocrine with diffuse marker expression; the rest were low neuroendocrine.
Membranous Nectin-4 expression was low or absent overall but higher in low neuroendocrine tumours (P < 0.001), while DLL3 and SLFN11 were overexpressed in the high neuroendocrine group. NECTIN4 amplification occurred in 21.9% (16 of 73). The authors say this supports further investigation of alternative therapeutic strategies; it does not show that any drug works.
- ASCL1-driven tumours were the largest group at 41.8%.
- High neuroendocrine tumours expressed DLL3 and SLFN11 more.
- Nectin-4 protein was low overall but higher in low neuroendocrine tumours.
- NECTIN4 amplification was found in 21.9%.
- Staining is hypothesis-generating; it does not establish treatment benefit.
Why it matters
It borrows a classification from small cell lung carcinoma for a rare bladder tumour that currently has little to guide treatment choice.
Don't overread it
A retrospective cohort with expression data cannot show that any phenotype responds to a given drug.
The statistics, in plain English
The tumour is rare, so the subgroups are small (5 to 33 cases each) and percentages are imprecise. Expression of a target on a slide is not the same as responding to a drug against it.
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