Context.—

The Ventana programmed death ligand-1 (PD-L1) SP142 immunohistochemical assay (IHC) is approved by the US Food and Drug Administration as the companion diagnostic assay to identify patients with locally advanced or metastatic triple-negative breast cancer for immunotherapy with atezolizumab, a monoclonal antibody targeting PD-L1.

Objective.—

To determine interobserver variability in PD-L1 SP142 IHC interpretation in invasive breast carcinoma.

Design.—

The pathology database was interrogated for all patients diagnosed with primary invasive, locally recurrent, or metastatic breast carcinoma on which PD-L1 SP142 IHC was performed from November 2018 to June 2019 at our institution. A subset of cases was selected using a computerized random-number generator. PD-L1 IHC was evaluated in stromal tumor-infiltrating immune cells using the IMpassion130 trial criteria, with positive cases defined as immunoreactivity in immune cells 1% or more of the tumor area. IHC was interpreted on whole slide images by staff pathologists with breast pathology expertise. Interobserver variability was calculated using unweighted κ.

Results.—

A total of 79 cases were assessed by 8 pathologists. Interobserver agreement was substantial (κ = 0.727). There was complete agreement among all 8 pathologists in 62% (49 of 79) of cases, 7 pathologists or more in 84% (66 of 79) of cases and 6 pathologists or more in 92% (73 of 79) of cases. In 4% (3 of 79) of cases, all of which were small biopsies, pathologists' interpretations were evenly split between scores of positive and negative.

Conclusions.—

The findings show substantial agreement in PD-L1 SP142 IHC assessment of breast carcinoma cases among 8 pathologists at a single institution. Further study is warranted to define the basis for discrepant results.

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Author notes

Our work was supported in part by a National Institutes of Health/National Cancer Institute Cancer Center Support Grant (P30CA008748).

Hanna is an advisor (non-compensated) with PathPresenter. Reis-Filho is an ad hoc member of the scientific advisory board of Roche Tissue Diagnostics/Ventana Medical Systems. The other authors have no relevant financial interest in the products or companies described in this article.

The abstract for this paper was presented at the 109th annual meeting of United States and Canadian Academy of Pathology; March 3, 2020; Los Angeles, California.