An exploratory post hoc analysis of the phase 3 IMpassion130 trial revealed that the VENTANA PD-L1 SP142 immunohistochemistry (IHC) assay, which is approved for PD-L1 expression in metastatic triple-negative breast cancer (TNBC), had subpar concordance compared with 2 other PD-L1 IHC assays, the Dako 22C3 and VENTANA SP263, which are approved for other cancer indications but not for use in TNBC. The findings were presented at the European Society for Medical Oncology (ESMO) Congress 2019 in Barcelona, Spain. 

Using the SP142 assay, the IMpassion 130 trial previously showed that atezolizumab plus nab-paclitaxel was clinically beneficial for patients with metastatic TNBC who had PD-L1 positive expression. 

For the exploratory analysis, a total of 614 patients (68%) from the intent-to-treat population of the IMpassion130 trial had adequate tissue and were therefore included in the biomarker-evaluable population. The SP142, 22C3, and SP263 IHC assays were performed via central testing.

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The analytical concordance between SP142 and the 2 other assays was below the required threshold of 90% for overall percent agreement (OPA), positive percent agreement (PPA), and negative percent agreement (NPA). Specifically, for the SP142 assay compared with the 22C3 assay, the OPA was 64%, PPA was 98%, and NPA was 34%, and for the SPA142 assay compared with the SP263 assay, the OPA was 69%, PPA was 98%, and NPA was 45%.

Patients who had both a PD-L1 positive SP142 assay and 22C3 or SP263 positive assay had the greatest progression-free survival (PFS) and overall survival (OS) benefit compared with having positive expression from 1 or none of the unapproved assays. In addition, the PFS and OS benefit for patients who were PD-L1 positive according to the SP242 assay was seen regardless of whether the tissue sample was from the primary or metastatic tissue site. 

Disclosure: The study presenter, Hope Rugo, MD, reported funding and travel support from F. Hoffmann-La Roche, Ltd. For a full list of disclosures, please refer to the study abstract.

Reference

  1. Rugo HS, Loi S, Adams S, et al. Performance of PD-L1 immunohistochemistry (IHC) assays in unresectable locally advanced or metastatic triple-negative breast cancer (mTNBC): Post-hoc analysis of IMpassion130. Presented at: European Society of Medical Oncology (ESMO) Congress 2019; September 27-October 1, 2019: Barcelona, Spain. Abstract LBA20.