The following article features coverage from the 2019 San Antonio Breast Cancer Symposium. Click here to read more of Cancer Therapy Advisor‘s conference coverage.

Pathologists in the real world may be assigning the wrong immune-cell score with PD-L1 assays to patients, which can lead to inappropriate treatment recommendations. The study findings were presented during a poster discussion at the 2019 San Antonio Breast Cancer Symposium (SABCS) in San Antonio, Texas.1

A total of 19 pathologists from 14 institutions were digitally sent stained slides for triple-negative breast cancer specimens and asked to score the samples as PD-L1 positive (≥ 1% immune cell staining) or negative (< 1% immune cell staining) and estimate the percentage of immune cell staining for positive samples. Specimens were stained using 2 PD-L1 expression assays from Ventana, SP142 and SP263, and a total of 68 slides for SP142 and 76 for SP263 were digitally sent to pathologists. 

The Ventana PD-L1 (SP142) assay is approved by the US Food and Drug Administration to determine which patients with locally advanced or metastatic triple-negative breast cancer have tumors that express PD-L1 and can therefore receive atezolizumab.2

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Pathologists interpreted the stain as PD-L1–positive for 78% of samples (range, 64% – 96%) with the SP263 assay and 58% (range, 41% – 81%) with the SP142 assay (P <.0001). Pathologists were in complete agreement for only 50% of samples with SP263 and 38% of samples with SP142, yielding an intraclass correlation coefficient of 0.513 for SP263 and 0.560 for SP142.

In addition, the researchers created a new method called Observers Needed to Evaluate Subjective Tests (ONEST). Using this, they found the overall percentage agreement appeared to plateau at 46% with 10 pathologists for SP263 and 41% with 9 pathologists for SP142. 

“With that overall percentage agreement at 40%, it suggests that over half of pathologists in real-world situations could be misaligning the patient immune cell score,” said poster discussant Ashley Cimino-Mathews, MD, associate professor of pathology and oncology at the Johns Hopkins University School of Medicine in Baltimore, Maryland.

Disclosure: Some authors of this study disclosed financial relationships with the pharmaceutical industry. For a full list of disclosures, please refer to the original abstract.

Read more of Cancer Therapy Advisor‘s coverage of SABCS by visiting the conference page.


  1. Reisenbichler ES, Han G, Pelekanou V, et al. Prospective multi-institutional evaluation of pathologist assessment of PD-L1 assays in triple negative breast cancer. Poster presentation at: 2019 San Antonio Breast Cancer Symposium; December 10-14, 2019; San Antonio, TX. Abstract PD5-01.
  2. FDA approves atezolizumab for PD-L1 positive unresectable locally advanced or metastatic triple-negative breast cancer [news release]. Silver Spring, MD: U.S. Food and Drug Administration; March 8, 2019. Accessed December 10, 2019.