Dr. Gatti-Mays on Selecting Between FDA-Approved Assays for PD-L1 Expression in Breast Cancer

Margaret E. Gatti-Mays, MD, MPH, FACP, assistant professor, Division of Medical Oncology, Department of Internal Medicine, Pelotonia Institute for Immuno-Oncology, The Ohio State University Comprehensive Cancer Center–James, discusses considerations for selecting between FDA-approved companion diagnostic assays for measuring PD-L1 expression in triple-negative breast cancer (TNBC).

Currently, the VENTANA PD-L1 (SP142) and the Dako PD-L1 (22C3) assays are approved to aid in the identification of patients with TNBC who are eligible to receive immunotherapy. ​The SP142 assay is approved as a companion diagnostic for atezolizumab (Tecentriq), whereas, the 22C3 assay is approved as a companion diagnostic for pembrolizumab (Keytruda) both in patients with TNBC. The assays evaluate slightly different components of the tumor microenvironment, and they utilize different thresholds for PD-L1 positivity, says Gatti-Mays.

As such, one assay may be preferred in select clinical scenarios vs the other, Gatti-Mays adds. For example, the 22C3 assay could be preferred in patients who are taxane naïve, says Gatti-Mays. Conversely, patients who received a taxane-based regimen, such as weekly paclitaxel, may be better suited to receive the SP142 assay, Gatti-Mays says. In patients who are likely to receive gemcitabine plus carboplatin, the 223C assay may be optimal, Gatti-Mays adds.

Ultimately, utilizing these assays in combination may be reasonable for certain patients, Gatti-Mays explains. However, some institutions may prefer to use the SP142 assay because it has been approved for a longer period, can often be completed in-house, and may yield quicker results compared with the 223C assay, Gatti-Mays concludes.