Comparison of SP142 and 22C3 PD-L1 assays in a population-based cohort of triple-negative breast cancer patients in the context of their clinically established scoring algorithms

Abstract

Background: Immunohistochemical (IHC) PD-L1 expression is commonly employed as predictive biomarker for checkpoint inhibitors in triple-negative breast cancer (TNBC). However, IHC evaluation methods are non-uniform and further studies are needed to optimize clinical utility.

Methods: We compared the concordance, prognostic value and gene expression between PD-L1 IHC expression by SP142 immune cell (IC) score and 22C3 combined positive score (CPS; companion IHC diagnostic assays for atezolizumab and pembrolizumab, respectively) in a population-based cohort of 232 early-stage TNBC patients.

Results: The expression rates of PD-L1 for SP142 IC ≥ 1%, 22C3 CPS ≥ 10, 22C3 CPS ≥ 1 and 22C3 IC ≥ 1% were 50.9%, 27.2%, 53.9% and 41.8%, respectively. The analytical concordance (kappa values) between SP142 IC+ and these three different 22C3 scorings were 73.7% (0.48, weak agreement), 81.5% (0.63) and 86.6% (0.73), respectively. The SP142 assay was better at identifying 22C3 positive tumors than the 22C3 assay was at detecting SP142 positive tumors. PD-L1 (CD274) gene expression (mRNA) showed a strong positive association with all two-categorical IHC scorings of the PD-L1 expression, irrespective of antibody and cut-off (Spearman Rho ranged from 0.59 to 0.62; all p-values < 0.001). PD-L1 IHC positivity and abundance of tumor infiltrating lymphocytes were of positive prognostic value in univariable regression analyses in patients treated with (neo)adjuvant chemotherapy, where it was strongest for 22C3 CPS ≥ 10 and distant relapse-free interval (HR = 0.18, p = 0.019). However, PD-L1 status was not independently prognostic when adjusting for abundance of tumor infiltrating lymphocytes in multivariable analyses.

Conclusion: Our findings support that the SP142 and 22C3 IHC assays, with their respective clinically applied scoring algorithms, are not analytically equivalent where they identify partially non-overlapping subpopulations of TNBC patients and cannot be substituted with one another regarding PD-L1 detection. Trial registration The Swedish Cancerome Analysis Network - Breast (SCAN-B) study, retrospectively registered 2nd Dec 2014 at ClinicalTrials.gov; ID NCT02306096.

Keywords: 22C3; Concordance; Gene expression; Immunohistochemistry; PD-L1; Patient outcome; SP142; TILs; Triple-negative breast cancer.

Conflict of interest statement

The authors declare no competing interests except for JH who has obtained speaker's honoraria or advisory board remunerations from Roche, Novartis, Pfizer, EliLilly, MSD, Veracyte and ExactSciences, has received institutional research support from Cepheid, Roche and Novartis and who is a co-founder and shareholder of Stratipath AB.

© 2023. BioMed Central Ltd., part of Springer Nature.

Figures

Fig. 1

Study flowchart. Our final cohort consisted of 232 early-stage TNBC patients recruited from the population-based SCAN-B cohort. Abbreviations TNBC: triple-negative breast cancer; NKBC: National Breast Cancer Quality (NKBC) registry; SCAN-B: Swedish Cancerome Analysis Network - Breast; TMA: tissue microarray; NACT: neoadjuvant chemotherapy

Fig. 2

Tissue microarray immunohistochemical (IHC) images of PD-L1 staining and comparison of assays. A:i Negative PD-L1 staining with SP142. A:ii Positive PD-L1 staining in immune cells (ICs) with the SP142 antibody. A:iii Positive 22C3 staining, mostly in ICs. ii and iii are from the same tumor. A:iv Positive PD-L1 staining in tumor cells and in ICs with the 22C3 antibody. All images at 20 × magnification. Concordance analyses in the overall cohort (N = 232) between the SP142 and 22C3 assays with different scoring algorithms where SP142 IC ≥ 1% is compared to 22C3 combined positive score (CPS) ≥ 10, 22C3 CPS ≥ 1 and to 22C3 IC ≥ 1% in (B–D), respectively. Venn diagrams show the overlap between the assay IHC expressions, kappa values represent the measurement of the level of agreement and the concordance rate equals the overall percentage agreement

Fig. 3

Association of immunohistochemical (IHC) PD-L1 expression with PD-L1 (CD274) gene expression (mRNA) in the overall cohort. In A–D the association of gene expression with SP142 PD-L1 staining in immune cells (ICs), 22C3 combined positive score (CPS) ≥ 1, 22C3 IC staining and 22C3 CPS ≥ 10, respectively, all at two-categorical IHC expressions. In E the association of gene expression with 22C3 CPS at three-categorical IHC expression. The mRNA expression of the SP142 IC and 22C3 CPS concordant and discordant cases in (F) and (G), with CPS threshold of 1 and 10, respectively

Fig. 4

Kaplan Meier survival analyses according to immunohistochemical PD-L1 status in the cohort receiving (neo)adjuvant chemotherapy. Invasive disease-free survival (IDFS), overall survival (OS) and distant relapse-free interval (DRFI) according to SP142 PD-L1 expression in immune cells (IC+) in panel (A) and in panel (B) for 22C3 combined positive score (CPS) at a threshold of 10

Fig. 5

Subgroup survival analysis of patients with 22C3 combined positive score (CPS) p-value for distant relapse-free interval (DRFI) according to SP142 PD-L1 status in the (neo)adjuvant chemotherapy sub-cohort that had 22C3 CPS < 10 (N = 119)