Alexandr Poprach

Small cell carcinoma of the bladder: why ADC targets from conventional UC do not simply carry over, and what may work instead 🧵 New in @Histo_Journal: 88 SmCCB from Milan and Erlangen, 79 fully profiled by IHC for ASCL1, NEUROD1, POU2F3, YAP1, HNF4α, NE and tuft cell markers, plus 7 therapeutic targets and NECTIN4 FISH. 🔬 Two phenotypes 🟢 High-NE (57/79): ASCL1-driven, NEUROD1-driven or mixed, diffuse synaptophysin, chromogranin and CD56 🟠 Low-NE (22/79): POU2F3-driven, YAP1-driven or TF-negative, weak or absent NE markers, significantly associated with admixed urothelial, glandular or squamous histology 🎯 ADC and BiTE targets, one by one Nectin-4 (membranous) • Completely negative in 75% (60/80) • Median H-score 0, mean 11.6, max 220 • Higher in Low-NE than High-NE (median 1.5 vs 0, P<0.001), consistent with retained urothelial differentiation NECTIN4 amplification (FISH) • 16/73 (21.9%), a frequency comparable to conventional UC • No difference between High-NE and Low-NE (P=0.835) • No association with membranous protein (P=0.099) TROP2 • Completely negative across the cohort HER2, FOLR1, Claudin 18.2 • Rare and weak expression only DLL3 • Positive in 35/43 evaluable High-NE cases (81%) • Nearly absent in Low-NE (P<0.001) • Relevant for DLL3-directed BiTEs such as tarlatamab and for DLL3 ADCs in development SLFN11 • Median H-score 125, significantly higher in High-NE (P=0.006) • Supports testing DNA-damaging strategies in this group 💡 Key takeaways 1️⃣ High-NE SmCCB is largely Nectin-4 protein negative, yet carries NECTIN4 amplifications at rates similar to conventional UC. The amplification is present, the protein is not. 2️⃣ Our hypothesis: this points to NE transdifferentiation from a urothelial precursor that already harboured the amplification. The gene status is retained, while the urothelial protein program, including Nectin-4, is switched off during lineage change. The equal amplification rate in both phenotypes fits this model. It needs confirmation in paired and clonal analyses. 3️⃣ Practical consequence: NECTIN4 FISH alone should not be read as a surrogate for target presence in SmCCB. Gene status and membranous protein both need to be assessed. 4️⃣ Enfortumab vedotin benefit cannot be assumed in High-NE SmCCB. Low-NE tumours with residual urothelial features remain the more plausible candidates for UC-type ADCs. 5️⃣ High-NE SmCCB behaves biologically like SCLC: DLL3-high, SLFN11-high. This makes it a rational population for SCLC-directed strategies. 6️⃣ A tuft cell-like subset exists: POU2F3-driven tumours co-express POU2AF2 (11/16) and ChAT (13/16), with preclinical mSWI/SNF vulnerabilities. 7️⃣ A simple workflow (NE markers ± TF panel) can stratify SmCCB in routine diagnostics today. ⚠️ Limits: retrospective, TMA-based, no treatment or outcome annotation. Treatment-annotated and paired pre/post-therapy cohorts are the next step. Big shout out to Nazario Tenace from San Raffaele he drove this work as fellow. Bright future for this talented pathologist. Shout out also at great collaborators from Sann Raffaele @AndreaNecchi @Albert0Briganti @F_Montorsi and @mauriziocollechia @maurilioponzoni @claudiodoglioni and @UroMoschini Great collaboration between San Raffaele Milan and UK Erlangen, led by Nazario Tenace, with @andreanecchi 🔗 doi.org/10.1111/his.70284

Our NECTIN4 scoring system for predicting enfortumab vedotin response in urothelial carcinoma is just published. 🔬 The short version: NECTIN4 is not a failed biomarker. It has been measured in the wrong compartment. 📊 179 EV-treated mUC patients, multicenter, FISH plus IHC, benchmarked against EV-301 EPAR data. Why the field thought NECTIN4 was ubiquitous 🧠 In EV-301 the median H-score was 250, with 82.6% ≥150. That near-universal expression underpinned the biomarker-unselected label. In our cohort, membranous H-score alone was 160. Cytoplasmic was 200. Combined, 260, with 78.2% ≥150, almost exactly mirroring EV-301. So the trial numbers most likely reflect membranous plus cytoplasmic staining. That single methodological choice is why NECTIN4 looked like it was everywhere. 🎯 And it matters, because only one compartment predicts anything: ✅ Membranous 2+/3+ vs 0/1+: ORR 55.1% vs 25.5% (p<0.001), mPFS 7.1 vs 2.9 months (HR 0.45), mOS 12.3 vs 6.9 months (HR 0.57). ❌ Cytoplasmic: ORR 49.6% vs 39.5% (p=0.4). No PFS or OS signal. ❌ Bulk NECTIN4 mRNA, which cannot resolve localisation: no association either. Adding cytoplasmic staining inflates positivity and dilutes prediction. Negativity rate drops from 12% to 3.4%. More positives, less information. 📉 The scoring system 🔬 Four tiers (0, 1+, 2+, 3+) adapted from the ASCO/CAP HER2 gastric algorithm, chosen deliberately because it accounts for incomplete membranous staining, the same framework that carried T-DXd to tumour-agnostic approval. Blinded interobserver testing, 44 cases, three raters, two with no prior NECTIN4 experience: 📈 Fleiss' κ 0.749 across all four tiers. 📈 Fleiss' κ 0.874 for the clinically relevant 0/1+ vs 2+/3+ cutoff. Almost perfect agreement. Reproducible, teachable in a short training session, deployable in routine practice. Genomics on top 🧬 NECTIN4 amplification in 25.1% (45/179). ORR 76.2% vs 36.6%. mPFS 12.2 vs 3.9 months (HR 0.40). mOS 30.1 vs 8.5 months (HR 0.33). At 24 months, 58.8% of amplified patients were alive versus 19.0%. And IHC prescreens for it: 80% of amplified tumours are 3+, under 5% of 0/1+ tumours carry an amplification. Restricting FISH to 2+/3+ captures 97.8% of amplified cases while sparing 29.1% of patients any molecular testing. ⚡ The integrated three-tier model: 1️⃣ Amplified: ORR 76.2%, mOS 30.1 mo 2️⃣ Non-amplified, membranous high: ORR 42.9%, mOS 8.8 mo 3️⃣ Non-amplified, membranous low: ORR 26.1%, mOS 6.9 mo Both remained independent in multivariable models. C-index for OS improves from 0.557 to 0.621 when amplification and membranous expression are combined. Neither marker alone does what the two do together. Where I think this lands 🎯 I do not (!) read this as an argument for testing every patient . With EV+P as first-line standard and few alternatives, a negative result rarely changes what you do today and shouldn't change it right now given the high EVP efficacy. But that is an argument about the therapeutic landscape, not about the biology. And the landscape is changing fast: HER2 ADCs, TROP2, HER3/EGFR, NECTIN4 radioligands and T-cell engagers. The moment two viable options compete for the same patient, the question stops being "does the target matter" and becomes "which target first." Notably, unlike the HER2-low paradigm, EV-301 showed an attenuated treatment effect in NECTIN4-low disease, PFS HR around 0.9 with confidence intervals crossing 1 (check out Figure 1 of the paper). ⚠️Prospective validation is running: EVOKE (DRKS00034745). Immense thanks to @niklas_kluemper and Jonas Saal, to Thomas Büttner, Sebastian Rauch and Fabienne Lange, and to every centre and biobank that contributed. This was a genuinely collaborative effort within the fantastic GUARDIANS and BRIDGE Consortium. 🙏 🔗 doi.org/10.1158/1078-0432.CC… @Uroweb @AmerUrological @ASCO @PathSoc @OncoAlert @Histo_Journal @andreanecchi @emanuele_crupi @danieleraggi83 @raffcolo @Dr_Aggen @DrRosenbergMSK @h_alahmadie @PGrivasMDPhD @shilpaonc @drenriquegrande @amerseburger @brookmans76 @DrYukselUrun @onkowissen @imedverse @UroDocAsh @urotoday @EUplatinum @JCO_ASCO @CCR_AACR @niklas_kluemper @DrRosenbergMSK @Dr_Aggen @Uromigos @tompowles1 @shilpaonc @PGrivasMDPhD #Uropathology #urothelial #BladderCancer #NECTIN4 #pathtwitter

Summary of my below post explaining uropathology for medical experts !

Overview on urothelial cell layer architectures and considerations on molecular subtypes of MIBC and mUC. ➡️from my previous thread: teapaw.org/markuseckstein3/status…