ADC + Immunotherapy Combinations: Choosing Patients With No Established Biomarker

ADC + Immunotherapy Combinations: Choosing Patients With No Established Biomarker

Antibody-drug conjugates (ADCs) have moved from late-line monotherapy into first-line combinations with checkpoint inhibitors. Enfortumab vedotin plus pembrolizumab is standard in advanced urothelial cancer, sacituzumab govitecan plus pembrolizumab was approved by the FDA for first-line PD-L1-positive triple-negative breast cancer (TNBC) in June 2026, and TROP2 ADC combinations are now reading out in lung cancer.

The hard part for translational and companion diagnostic (CDx) teams is patient selection. The obvious biomarker for an ADC is its target, yet for TROP2 ADCs conventional immunohistochemistry (IHC) has not reliably separated responders from non-responders. Add a checkpoint inhibitor and you have two drugs, two mechanisms and possibly two tests. This article covers the evidence, the HER2-low precedent, the move to computational pathology, and how to build a biomarker strategy when no established marker exists.

Key takeaways

• ADC payloads can induce immunogenic cell death, the main preclinical rationale for combining ADCs with checkpoint inhibitors.
• Approved TROP2 ADC indications do not require a TROP2 test; benefit has not tracked closely with conventional TROP2 IHC.
• Where approved combinations use a biomarker, it has been PD-L1 for the checkpoint inhibitor, not the ADC target.
• HER2-low showed an existing IHC assay can be re-cut at the low end of expression, and how hard that end is to score reproducibly.
• The TROP2 normalised membrane ratio (NMR), read by computational pathology, is the first prospective quantitative IHC CDx being tested for an ADC.

Why combine ADCs with checkpoint inhibitors?

Immunogenic cell death. Microtubule inhibitor payloads (MMAE, DM1) and topoisomerase I inhibitor payloads (such as deruxtecan) can cause immunogenic cell death, promoting dendritic cell activation and antigen presentation. In mouse models, trastuzumab emtansine made HER2-positive tumours highly susceptible to CTLA-4 and PD-1 blockade (Müller et al., Science Translational Medicine, 2015), and trastuzumab deruxtecan enhanced antitumour immunity and combined beneficially with anti-PD-1 and anti-CTLA-4 antibodies (Iwata et al., PLoS ONE, 2019).

Bystander killing. Membrane-permeable payloads diffuse into neighbouring cells, so an ADC can kill target-low cells next to target-positive ones. That helps in heterogeneous tumours, and it is the first reason target expression is a weak selection biomarker.

Clinical proof of concept. In EV-302, enfortumab vedotin plus pembrolizumab improved median overall survival versus platinum chemotherapy in untreated advanced urothelial cancer (31.5 vs 16.1 months; HR 0.47). The FDA approved the combination in December 2023 without requiring a Nectin-4 or PD-L1 test.

The TROP2 ADC landscape in October 2026

ASCENT-04/KEYNOTE-D19 randomised 443 patients with untreated PD-L1-positive (CPS ≥10) metastatic TNBC to sacituzumab govitecan plus pembrolizumab or chemotherapy plus pembrolizumab: median PFS 11.2 vs 7.8 months (HR 0.65). On 24 June 2026 the FDA approved the combination for CPS ≥10 tumours, alongside monotherapy for patients not eligible for PD-1/PD-L1 therapy (ASCENT-03). The selection test is PD-L1; no TROP2 test is involved.

OptiTROP-Lung05 randomised 413 Chinese patients with PD-L1 TPS ≥1% NSCLC to sacituzumab tirumotecan plus pembrolizumab or pembrolizumab alone. At interim analysis, published in The Lancet, the PFS HR was 0.35 (median not reached vs 5.7 months), with benefit at TPS 1–49% and ≥50%. Overall survival is immature, and the application is under priority review in China.

AVANZAR compares datopotamab deruxtecan plus durvalumab and carboplatin with pembrolizumab plus chemotherapy in first-line NSCLC. Its dual primary endpoints include a TROP2 biomarker-positive population, making it the first large test of whether a TROP2 biomarker improves selection for an ADC plus checkpoint inhibitor. At the time of writing, results had not been announced.

The patient-selection problem: target expression is not response

TROP2 is expressed in most epithelial cancers, so conventional IHC produces few truly negative tumours. In the phase 3 ASCENT trial in pretreated TNBC, a prespecified analysis by H-score found benefit over chemotherapy across TROP2 expression levels, with numerically smaller benefit in the small low-expression group (Bardia et al., Annals of Oncology, 2021). Neither sacituzumab govitecan nor datopotamab deruxtecan labels require TROP2 testing.

Why does target expression IHC underperform?

• Bystander payloads reduce dependence on uniform expression.
• Internalisation matters: the ADC needs membrane TROP2 that is taken up and processed, not just total protein.
• Payload sensitivity (topoisomerase I dependence, DNA repair, efflux pumps) varies independently of target level.
• Semi-quantitative scores compress a continuous variable into categories with limited reproducibility.

Add a checkpoint inhibitor and benefit may come from the ADC, the immunotherapy or their interaction, which trial designs rarely separate.

The HER2-low precedent

In August 2022 the FDA approved trastuzumab deruxtecan for HER2-low breast cancer (IHC 1+ or 2+/ISH-negative) based on DESTINY-Breast04, with the Ventana PATHWAY anti-HER2/neu (4B5) assay as the CDx. In January 2025 it extended approval to HR-positive HER2-low or HER2-ultralow disease (DESTINY-Breast06), and the 4B5 label was expanded to identify HER2-ultralow tumours.

Three lessons carry over:

1. The assay was built for a different decision. HER2 IHC was designed to find overexpression. Separating 0 from 1+ and ultralow puts weight on its least reproducible range.
2. Cut-offs move. HER2-low became HER2-ultralow within three years, so ADC assays should report a continuous value, not just a binary call.
3. Standardisation is part of the product. Pathologist training and external quality assessment should be planned from the start.

Similar questions are arriving in gastric cancer: claudin 18.2 already has an IHC CDx for the antibody zolbetuximab, and claudin 18.2 ADCs are in development. Whether a cut-off set for a naked antibody suits an ADC with a bystander payload should be tested, not assumed.

Computational pathology: the TROP2 NMR approach

AstraZeneca’s Quantitative Continuous Scoring (QCS) platform asks where TROP2 sits rather than how much is present. It segments every tumour cell on a digitised slide and calculates a normalised membrane ratio: membrane TROP2 relative to total membrane plus cytoplasmic TROP2. A tumour is positive if at least 75% of tumour cells have a ratio of 0.56 or below.

In an exploratory analysis of TROPION-Lung01, QCS-NMR-positive non-squamous patients without actionable alterations had a PFS HR of 0.52 for datopotamab deruxtecan versus docetaxel (7.2 vs 4.1 months), against 0.75 in the overall population.

The diagnostic follow-through matters for the CDx industry. In April 2025 the FDA granted Breakthrough Device designation to Roche’s VENTANA TROP2 (EPR20043) RxDx Device, combining an IHC assay, Roche scanners, the navify image management system and a QCS-based algorithm. It is used in AVANZAR and TROPION-Lung10, and in TROPION-Lung17, a phase 3 trial started in January 2026 that enrols only NMR-positive patients.

Two cautions: the cut-off was optimised retrospectively, so prospective validation is what counts; and the algorithm, scanner and software are all regulated parts of the CDx, raising questions about locked algorithms and scanner equivalence.

Where PD-L1 fits

If both markers are needed, eligibility could depend on two IHC assays with different scoring systems (CPS, TPS, NMR) from one small biopsy, making tissue stewardship and multiplex workflows operational priorities. See our analysis of PD-L1 as a predictive biomarker.

Building a biomarker strategy for an ADC + IO programme

• Plan for an all-comer label with an embedded hypothesis. EV-302 shows ADC combinations can win without selection. Where the hypothesis is strong, power a biomarker population as a dual primary endpoint, as AVANZAR does; exploratory analyses rarely support a CDx claim.
• Digitise tissue from day one. Mandate baseline tissue, record pre-analytical variables and scan every slide, so a quantitative score can be developed later without re-staining.
• Measure target biology, not just level. Score localisation, heterogeneity and spatial distribution as continuous variables, alongside payload-sensitivity and immune-context markers. The spatial biology toolkit suits this work.
• Separate the components. Where designs allow, test whether a marker predicts benefit from the ADC, the checkpoint inhibitor or the combination. Regulators will ask which drug the test selects for.
• Bring in the CDx partner before phase 3. A computational pathology CDx needs a locked algorithm and multi-site, multi-scanner validation before pivotal enrolment. See our FDA companion diagnostic approval guide and our article on pharma-diagnostics co-development partnerships.

What IHC and digital pathology vendors should offer

• Assays validated at the low and subcellular expression levels where cut-offs actually fall.
• Continuous, quantitative outputs that can be re-thresholded as data mature.
• Regulatory-grade algorithms with change-control plans, scanner equivalence data and a route through FDA, EU IVDR and MHRA.
• Workflows that deliver PD-L1 and ADC target scores from limited tissue.
• Pathologist training and external quality assessment, learning from HER2-low.
• Retrospective reanalysis of digitised trial archives, often where the next biomarker is found.

For the EU route, our IVDR companion diagnostics guide covers the requirements for software-driven CDx.

ADC x IO at ImmunoMark London

These questions span both streams at the immuno-oncology and companion diagnostics conference in London on 3–4 March 2027, with 400+ senior pharma, biotech and diagnostics leaders expected. The agenda includes “Keynote: Next-Gen Combo Immunotherapies” from Ivan Diaz-Padilla, Senior Vice President, Global Head of Oncology R&D, Ipsen, in Stream 1, and “Digital Pathology & Spatial Transcriptomics in Oncology” and “Companion Diagnostics Co-development Strategies” in Stream 2: Biomarkers & Companion Diagnostics. Formats include keynotes, panels, case studies, pre-arranged 1:1 meetings and a Day 1 drinks reception. For the wider week, see our guide to London precision oncology week.

Register for ImmunoMark London 2027

If your company wants to meet this audience directly, whether you develop IHC assays, digital pathology algorithms or CDx services for ADC programmes, see the London 2027 sponsorship opportunities or our overview of the companion diagnostics conference in London.

FAQs

Do TROP2 ADCs require a TROP2 test?

No. Approved indications for sacituzumab govitecan and datopotamab deruxtecan do not require TROP2 testing, because conventional TROP2 IHC has not reliably predicted benefit. A computational pathology CDx based on the TROP2 normalised membrane ratio is being used prospectively in phase 3 lung cancer trials of datopotamab deruxtecan.

Why combine an antibody-drug conjugate with immunotherapy?

Several ADC payloads cause immunogenic cell death, which can prime antitumour immunity, and preclinical studies showed enhanced activity with checkpoint inhibitors. Clinically, enfortumab vedotin plus pembrolizumab improved survival in first-line urothelial cancer, and sacituzumab govitecan plus pembrolizumab improved progression-free survival in first-line PD-L1-positive TNBC.

What is the TROP2 normalised membrane ratio?

A computational pathology score that measures, for each tumour cell, membrane TROP2 relative to total membrane and cytoplasmic TROP2. A tumour is positive if at least 75% of tumour cells have a ratio of 0.56 or below. In an exploratory TROPION-Lung01 analysis, positive non-squamous patients had a PFS hazard ratio of 0.52 with datopotamab deruxtecan versus docetaxel.

What does HER2-low teach about ADC biomarkers?

That an existing IHC assay can be re-cut at the low end of expression to define a new population, with the Ventana 4B5 assay as the CDx for trastuzumab deruxtecan. It also showed that low-end scoring is hard to reproduce and that cut-offs move, as the 2025 extension to HER2-ultralow demonstrated.

Is PD-L1 used to select patients for ADC and checkpoint inhibitor combinations?

Sometimes. Sacituzumab govitecan plus pembrolizumab is approved in first-line TNBC for PD-L1 CPS of 10 or more, while enfortumab vedotin plus pembrolizumab in urothelial cancer needs no PD-L1 test. So far PD-L1 has governed the checkpoint inhibitor, not the ADC.