PD-L1 Immunohistochemistry Assay Comparison in Atezolizumab Plus nab-Paclitaxel–Treated Advanced Triple-Negative Breast Cancer

Abstract

Background In the Phase III IMpassion130 study, atezolizumab plus nab-paclitaxel (A+nP) showed clinical benefit in advanced/metastatic triple-negative breast cancer (TNBC) patients who were programmed death-ligand 1 (PD-L1) + (tumor-infiltrating immune cells [IC] ≥1%) using the SP142 immunohistochemistry (IHC) assay. Here we evaluate 2 other PD-L1 assays for analytical concordance with SP142 and patient-associated clinical outcomes. Methods Samples from 614 patients (68.1% of intention-to-treat population) were centrally evaluated by IHC for PD-L1 status on IC (VENTANA SP142, SP263, Dako 22C3) or as a combined positive score (CPS; 22C3). Results Using SP142, SP263, and 22C3 assays, PD-L1 IC ≥ 1% prevalence was 46.4% (95% confidence interval [CI] = 42.5–50.4%), 74.9% (95% CI = 71.5–78.3%), and 73.1% (95% CI = 69.6–76.6%), respectively; 80.9% were 22C3 at CPS ≥1. At IC ≥ 1% (+), the analytical concordance between SP142 and SP263 and 22C3 was 69.2% and 68.7%, respectively. Almost all SP142+ cases were captured by other assays (double positive), but several SP263 + (29.6%) or 22C3 + (29.0%) cases were SP142– (single positive). A+nP clinical activity vs placebo+nP in SP263+ and 22C3+ patients (progression-free survival [PFS] hazard ratios [HRs] = 0.64–0.68; overall survival [OS] HRs = 0.75–0.79) was driven by double-positive (PFS HRs = 0.60–0.61; OS HRs = 0.71–0.75) rather than single-positive cases (PFS HRs = 0.68–0.81; OS HRs = 0.87–0.95). Concordance for harmonized cutoffs for SP263 (IC ≥ 4%) and 22C3 (CPS ≥10) to SP142 IC ≥ 1% was subpar (approximately 75%). Conclusions 22C3 and SP263 assays identified more patients as PD-L1 + (IC ≥ 1%) than SP142. No inter-assay analytical equivalency was observed. Consistent improved A+nP efficacy was captured by the SP142 PD-L1 IC ≥ 1% subgroup nested within 22C3 and SP263 PD-L1 + (IC ≥ 1%) populations.

Discordance of PD-L1 Expression at the Protein and RNA Levels in Early Breast Cancer

“…In comparison, previous comparative studies have been limited in that they mostly evaluated the PD-L1 IHC expression using different antibody clones with the sole focus on TNBC [22,23]. In line with previous results [6], we show here that PD-L1 positivity was highly concordant between SP142 and SP263 immunohistochemical antibodies, while the observed level of discordance varied depending on the applied method.…”

“…Pivotal randomized studies have demonstrated the efficacy of combined chemoimmunotherapy using immune checkpoint inhibition for both early and metastatic triplenegative breast cancer (TNBC) [1][2][3][4]. Robust predictive biomarkers are currently lacking, with PD-L1 protein expression showing inconsistent clinical utility for benefit at the metastatic setting [1,5] and varying concordance when assessed by different clones [6].…”

“…Potential causes for the reported inconsistency include assay performance [6]; a potentially lesser role of immunoediting at the primary tumor compared with the distant metastasis, further supported by the lower PD-L1 positivity rates at metastasis compared to primary tumor [9] and the fact that PD-L1 positivity at the metastasis carried potentially stronger predictive information in the IMPassion130 trial [7]; and heterogeneity of PD-L1 expression. In support of the latter, we have previously demonstrated that PD-1/PD-L1 expression is associated with discrepant prognostic values depending on the level of expression, mRNA, or protein [10,11].…”

Tumor Microenvironment in Breast Cancer—Updates on Therapeutic Implications and Pathologic Assessment

“…The Dako PD-L1 IHC 22C3 pharmDx assay defined PD-L1 positivity as a combined positive score of ≥1, while in the Ventana PD-L1 IHC SP142 assay, positivity was defined as ≥1 % expression in tumor-infiltrating immune cells (Figure 5) (Table A1). The different assays have been specifically implemented in relation to the clinical evidence from trials and validated with specific platforms [177][178][179]. Regardless, in addition to specific companion diagnostics, 22C3 (Dako) and SP263 (Ventana) are antibody clones generally accepted by pharmaceuticals for clinical use.…”

Standardization of PD-L1 immunohistochemistry

“…The immunohistochemistry (IHC) assays for PD-L1 have been a source of great uncertainty in both oncologists and pathologists. The wide range of FDA-approved assays with differential sensitivity and scoring system 1 , and the lack of success in harmonization of these assays 2,3 has led to confusion in pathology labs. Currently, in breast cancer, the oncologist's treatment plan must either be known in advance of the assay performance, or two non-concordant assays (Ventana SP142 and Agilent 22c3) must be performed since each qualifies patients for different PD-1 axis therapy (Atezolizumab and Pembrolizumab, respectively).…”