Tumor Immune Response as a Biomarker for Metastasis-Free Survival of Breast Cancer and Immune Checkpoint Inhibition Therapy: A Retrospective Cohort Study.

BACKGROUND

Breast cancers (BRCs) can be classified into 6 molecular subtypes based on gene expression profiles. Previous research suggests that tumor-infiltrating lymphocytes are associated with metastasis-free survival (MFS) in triple-negative and HER2-overexpressing BRC.

OBJECTIVES

Our study aims to investigate further how the immune response (IR) may impact MFS in different molecular subtypes of BRC.

DESIGN

A single hospital-based retrospective cohort study.

METHODS

A training series of 327 BRCs was used to identify 297 IR transcripts that were correlated with the T cell-associated CD3D transcript or the B cell-associated CD19 transcript. Using these IR transcripts, each of the 6 molecular subtypes was hierarchically clustered into high and low immune responders. An IR score based on the average of the 297 IR transcripts was determined for each BRC. Correlations between the IR score and 3 signatures for IR or response to immune checkpoint inhibition therapy (ICIT) were investigated. A series of 884 BRCs from public datasets was used for confirmation, and the other independent series of 988 BRCs was used for validation.

RESULTS

For subtype I, high immune responders had a statistically significantly better MFS than low immune responders in all the training, confirmation, and validation series by Kaplan-Meier survival analysis ( = .0039, .049, .039, log-rank test). The same trend was observed for subtype II ( = .16, .052, .015) and subtype IV ( = .0078, .0002, .12). Our IR scores were linearly correlated with the Teschendorff, the T-effector and IFNg, and the T-cell inflamed signatures for IR or ICIT. The IR scores were also linearly correlated with the expression of 6 different immune checkpoint genes.

CONCLUSIONS

Tumor IR is a biomarker for MFS for BRCs of I, II, and IV subtypes. Our study supports the potential use of the IR score for identifying patients responsive to ICIT.