Abstract P6-06-21: A 5-gene predictor of triple negative breast cancer outcome that also correlates with immune checkpoint receptor expression
Authors: Yau C , Campbell M , Esserman L , Benz CC 
Published: August 2014

Background: It is becoming increasingly clear that immune responses play an important role in determining triple negative (Tneg) breast cancer prognosis. Thus, emerging immunotherapeutic strategies, such as targeting immune checkpoint co-receptors (e.g. CTLA4 or PD-1), offer an attractive novel approach. However, to date, there are no established predictive biomarkers to identify Tneg patients most likely to benefit from these immunotherapies. We recently identified a 5-gene prognostic signature (TNFRSF17, CLIC5, HLA-F, CXCL13, XCL2), referred to as the Integrated Cytokine Score (ICS). Interestingly, the ICS showed functional linkage through both type 1 (interferon-γ (IFNG)) and type 2 (IL-10) immune response pathways. Here, we hypothesized that the ICS would be associated with the expression of IFNG as well as immune checkpoint genes and may therefore serve as a surrogate biomarker for targeted immunotherapies.

Method: Transcriptome data from a set of 94 node negative chemotherapy naïve Tneg tumors were pooled from three independent microarray datasets (GSE2034, GSE5327 and GSE7930). The ICS was computed as the scaled sign-corrected average of the 5 signature genes, such that a high ICS is indicative of low immune function, which in turn translates to a higher recurrence risk. We explored the correlation between the ICS and the expression of IFNG, IL-10 and 3 different immune checkpoint co-receptor genes: CTLA4 (cytotoxic T-lymphocyte antigen 4), PD-1/PDCD1 (programmed cell death protein-1) and LAG3 (lymphocyte activation gene 3). In addition, Cox proportional hazard modeling was used to evaluate the association with distant metastasis free survival (DMFS).

Results: The ICS is significantly prognostic (hazard ratio associated with 1 standard deviation increase = 1.48 (1.04 - 2.10), p = 0.03). ICS strongly anti-correlated (p&lt;0.05) with IFNG (r = -0.66), CTLA4 (r = -0.38), PD-1/PDCD1 (r = -0.25) and LAG3 (r = -0.60) expression. Interestingly, despite this strong correlation and the prognostic significance of the ICS, none of these four immune genes were significantly associated with Tneg DMFS (p = 0.31 - 0.86). IL-10 expression was not correlated with ICS (r = -0.04) or DMFS (p = 0.43).

Conclusion: Our current findings suggest that Tneg tumors with a low ICS have elicited a type-1 (IFNG pathway) antitumor immune response. However, since the tumor is essentially “self”, this results in the activation of negative immunoregulatory networks that prevent autoimmunity (checkpoint co-receptors). Thus, the prognostic 5-gene ICS may also be a useful biomarker for immune checkpoint blockade, which could become an alternative therapeutic strategy to traditional chemotherapy for low-ICS Tneg patients who are at reduced risk of metastatic recurrence. In contrast, we propose that high-ICS Tneg tumors do not elicit type-1 antitumor immune responses or subsequent immunoregulatory network activation. For these high-ICS patients at increased risk of metastatic recurrence, additional immunotherapeutic approaches capable of enhancing both recruitment and activation of immune effector cells, as well as checkpoint blockade, may be necessary.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P6-06-21.