Role of Cytotoxic Tumor-Infiltrating Lymphocytes in Predicting Outcomes in Metastatic HER2-Positive Breast Cancer: A Secondary Analysis of a Randomized Clinical Trial

Abstract

Importance: Accumulating evidence indicates that tumor-infiltrating lymphocytes (TILs) are associated with clinical outcomes and may predict the efficacy of chemotherapy and human epidermal growth factor receptor 2 (HER2, encoded by the gene ERBB2)-targeted therapy in patients with HER2-positive breast cancer.

Objective: To investigate the role of TILs, particularly cytotoxic CD8+ T cells, in the prediction of outcomes in patients with HER2-positive metastatic breast cancer randomized to an antibody-based (trastuzumab) vs a small molecule-based (lapatinib) anti-HER2 therapy.

Design, setting, and participants: The Canadian Cancer Trials Group MA.31 phase 3 clinical trial accrued patients from 21 countries and randomized 652 with HER2-positive metastatic breast cancer to receive trastuzumab or lapatinib, in combination with a taxane, from January 17, 2008, through December 1, 2011. Patients had received no prior chemotherapy or HER2-targeted therapy in the metastatic setting. The median follow-up was 21.5 months (interquartile range, 14.3-31.0). The tumor tissue collected for primary diagnosis was used in this ad hoc substudy. Sections were scored for TILs on hematoxylin-eosin (H&E)-stained sections, and immunohistochemical analysis was performed to assess CD8, FOXP3, CD56, and programmed cell death protein 1 (PD-1) expression on stromal (sTILs) and intratumoral TILs. Data were analyzed from July 15, 2015, through July 27, 2016.

Interventions: Treatment with trastuzumab or lapatinib in combination with taxane chemotherapy (paclitaxel or docetaxel) for 24 weeks.

Main outcomes and measures: Prognostic effects of biomarkers were evaluated for progression-free survival by stratified univariate log-rank test with Kaplan-Meier curves and by multivariate Cox proportional hazards regression; predictive effects were examined with a test of interaction between treatment allocation and biomarker classification.

Results: Of the 647 treated women (mean [SD] age, 55.0 [10.8] years), 614 had tumor tissue samples scored for H&E sTILs and 427 for CD8 biomarker assessments. Overall H&E sTIL counts of greater than 5% (high) were present in 215 cases (35%) but did not show significant prognostic or predictive effects. Univariate stratified analyses detected a significant predictive effect on risk for progression with lapatinib compared with trastuzumab among patients with low CD8+ sTIL counts (observed hazard ratio, 2.94; 95% CI, 1.40-6.17; P = .003) and among those with high CD8+ sTIL counts (observed hazard ratio, 1.36; 95% CI, 1.05-1.75; P = .02), confirmed in stepwise multivariate analysis (interaction P = .04). Other immunohistochemistry biomarkers were not associated with prognostic or predictive effects.

Conclusions and relevance: In this secondary analysis of a phase 3 randomized clinical trial, a low level of preexisting cytotoxic sTILs predicted the most benefit from an antibody- vs a small molecule-based drug against the same target.

Trial registration: clinicaltrials.gov Identifier: NCT00667251.

Conflict of interest statement

Conflict of Interest Disclosures: Dr Gelmon reports serving in an advisory role for Novartis, Pfizer, AstraZeneca, and Genentech. Dr Nielsen reports holding a proprietary interest in the Prosigna intrinsic subtype classifier (not used in this study) and receiving consultancy fees from NanoString Technologies. No other disclosures were reported.

Figures

Figure.. Progression-Free Survival (PFS) Associations of Immune Infiltrates in the Original Biopsy Tissue Specimens From the Canadian Cancer Trials Group (CCTG) MA.31 Trial Population With Metastatic HER2-Positive Breast Cancer

Prognosis (including both randomization arms) is depicted with Kaplan-Meier curves for total stromal tumor-infiltrating lymphocyte (TIL) counts (high indicates >5% median score value) (A) and for CD8+ cytotoxic TILs (positive indicates a mean of ≥3 stromal CD8+ TILs per 0.6-mm diameter tissue disc, assessed by immunohistochemical analysis on tissue microarrays or 0.6-mm discs digitally extracted from full-face sections) (B). Predictive capacity for PFS is stratified by treatment with trastuzumab vs lapatinib in CCTG MA.31 study patients with low (C) or high (D) levels of CD8+ stromal TILs in their primary tumor specimen.