# PD-L1 IHC 22C3 pharmDx

Source: https://onco.cc/drugs/dako-pd-l1-22c3-pharmdx/  
OnCo record `dako-pd-l1-22c3-pharmdx` (Treatment). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

The 22C3 pharmDx assay is the PD-L1 stain tied to pembrolizumab since 2015 and the source of the combined positive score (CPS). The cut-off differs by cancer: 1% of tumour cells in lung cancer, CPS 1 in gastric, cervical and head and neck cancer, CPS 10 in oesophageal and triple-negative breast cancer, so one stain is read differently per disease.

## Summary

Approved 2 October 2015 (PMA P150013, Dako, now Agilent) as the companion diagnostic for pembrolizumab in non-small-cell lung cancer, initially at TPS ≥50% and from 2016 at TPS ≥1%. It has since been approved for gastric and gastro-oesophageal junction cancer (CPS ≥1, 2017), cervical cancer (CPS ≥1, 2018), head and neck squamous cell carcinoma (CPS ≥1, 2019), oesophageal squamous cell carcinoma (CPS ≥10, 2019) and triple-negative breast cancer (CPS ≥10, 2020, KEYNOTE-355). The many cut-offs are a source of confusion for patients: the same stain is read differently depending on the cancer and the trial that set the threshold.

## Fields

- Kind: Treatment
- Status: approved
- Last checked: 2026-09-10
- Tags: test
- Brand: PD-L1 IHC 22C3 pharmDx
- Modality: PD-L1 immunohistochemistry companion diagnostic assay
- Mechanism: Mouse monoclonal antibody 22C3 on the Dako Autostainer Link 48, reported as tumour proportion score (TPS) in lung cancer or combined positive score (CPS, tumour plus immune cells relative to tumour cells) in other cancers.
- Approvals: US 2015: Companion diagnostic for pembrolizumab in NSCLC (TPS); US 2017: Gastric / GEJ adenocarcinoma, CPS ≥1; US 2019: Head and neck squamous cell carcinoma (CPS ≥1) and oesophageal squamous cell carcinoma (CPS ≥10); US 2020: Triple-negative breast cancer, CPS ≥10 (pembrolizumab plus chemotherapy)

## Notes

- What a result means: the report gives a TPS or CPS; whether it counts as 'positive' depends on the drug label for your cancer, so the same number can be positive in one cancer and negative in another.

## Sources

- FDA PMA P150013: https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfpma/pma.cfm?id=P150013
- Agilent: PD-L1 IHC 22C3 pharmDx: https://www.agilent.com/en/product/pharmdx/pd-l1-ihc-22c3-pharmdx

## Connected records

- cancers: [Cervical cancer](https://onco.cc/cancers/cervical/), [Gastric & gastro-oesophageal junction cancer](https://onco.cc/cancers/gastric/), [Head and neck squamous cell carcinoma](https://onco.cc/cancers/head-and-neck/), [Metastatic triple-negative breast cancer](https://onco.cc/cancers/tnbc-metastatic/), [Non-small-cell lung cancer](https://onco.cc/cancers/nsclc/), [Oesophageal cancer](https://onco.cc/cancers/esophageal/), [Triple-negative breast cancer (TNBC)](https://onco.cc/cancers/tnbc/)
- technologies: [Companion diagnostics](https://onco.cc/technologies/companion-diagnostic/), [Histopathology & immunohistochemistry](https://onco.cc/technologies/histopathology-ihc/)
- targets: [PD-L1](https://onco.cc/targets/pdl1/)
- drugs: [Pembrolizumab](https://onco.cc/drugs/pembrolizumab/), [VENTANA PD-L1 (SP142) Assay](https://onco.cc/drugs/ventana-pd-l1-sp142/)
- companies: [Agilent Technologies (Dako)](https://onco.cc/companies/agilent/)
- terms: [Combined positive score (CPS)](https://onco.cc/terms/cps/), [Immunohistochemistry (IHC)](https://onco.cc/terms/ihc/), [PD-L1 expression testing (22C3, SP142, SP263)](https://onco.cc/terms/pd-l1-testing/)
- key papers: [Comparison of SP142 and 22C3 PD-L1 assays in a population-based cohort of triple-negative breast cancer patients in the context of their clinically established scoring algorithms](https://onco.cc/key-papers/paper-sigurjonsdottir-sp142-22c3-tnbc-bcr-2023/), [PD-L1 Immunohistochemistry Assay Comparison in Atezolizumab Plus nab-Paclitaxel-Treated Advanced Triple-Negative Breast Cancer](https://onco.cc/key-papers/paper-rugo-pd-l1-assay-comparison-impassion130-jnci-2021/), [Pembrolizumab plus chemotherapy versus placebo plus chemotherapy for previously untreated locally recurrent inoperable or metastatic triple-negative breast cancer (KEYNOTE-355): a randomised, placebo-controlled, double-blind, phase 3 clinical trial](https://onco.cc/key-papers/paper-keynote-355-lancet-2020/)
- biomarkers: [PD-L1 CPS (combined positive score)](https://onco.cc/biomarkers/pd-l1-cps/), [PD-L1 TPS (tumour proportion score)](https://onco.cc/biomarkers/pd-l1-tps/)
- roadmaps: [Diagnostics roadmap: stains → gene panels → blood tests that decide treatment](https://onco.cc/roadmaps/diagnostics-roadmap/)

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