Towards predictive biomarkers for immunotherapy response in breast cancer patients

Src Kinase Is Biphosphorylated at Y416/Y527 and Activates the CUB-Domain Containing Protein 1/Protein Kinase C δ Pathway in a Subset of Triple-Negative Breast Cancers

Targeted therapeutics are needed for triple-negative breast cancer (TNBC). In this study, we investigated the activation of Src family of cytoplasmic tyrosine kinases (SFKs) and two SFK substrates-CUB-domain containing protein 1 (CDCP1) and protein kinase C δ (PKCδ)-in 56 formalin-fixed, paraffin-embedded (FFPE) TNBCs. Expression of SFK phosphorylated at Y416 (SFK_pY416⁺) in tumor cells was strongly associated with phosphorylation of CDCP1 and PKCδ (CDCP1_ pY743⁺ and PKCδ_pY311⁺), as assessed by immunohistochemistry, indicating increased SFK activity in situ. To enable biochemical analysis, protein extraction from FFPE tissue was optimized. Cleaved CDCP1 isoform (70 kDa) was expressed to a varying degree in all samples but only phosphorylated in TNBC tumor cells that expressed SFK_pY416. Interestingly, active SFK was found to be biphosphorylated (SFK_pY416⁺/pY527⁺). Biphosphorylated active SFK was observed more frequently in forkhead box protein A1 (FOXA1)^- TNBCs. In addition, in SFK_pY416^- samples, FOXA1⁺ TNBC tended to be SFK_pY527⁺ (classic inactive SFK), and FOXA1^- TNBC tended to be SFK_pY527^- (SFK poised for activation). Strong SFK_pY416 staining was also observed in tumor-infiltrating lymphocytes in a subset of TNBCs with high tumor-infiltrating lymphocyte content. This report will facilitate protein biochemical analysis of FFPE tumor samples and justifies the development of therapies targeting the SFK/CDCP1/PKCδ pathway for TNBC treatment.

Biomarker predictors for immunotherapy benefit in breast: beyond PD-L1

PURPOSE OF REVIEW

Immune checkpoint blockade (ICB) has changed the clinical course of multiple cancer types and durable responses have now been observed in breast cancer (BC) patients. Most data suggest that, compared to other subtypes, triple-negative BC (TNBC) patients are more responsive to ICB, and anti-PD-L1 therapy is now approved in PD-L1+ metastatic TNBC, in combination with chemotherapy.

RECENT FINDINGS

Nearly 40% of PD-L1+ TNBC patients did not respond to this combination. Thus, additional biomarkers appear to be necessary to more precisely identify potential responders. A comprehensive analysis of the breast tumor microenvironment (TME) and peripheral blood may identify potential biomarkers for a more accurate selection of patients likely to respond to ICB.

SUMMARY

Herein, we summarize key features of the breast TME, and beyond, that may hold predictive power in determining immunotherapy benefit. Incorporation of these features in controlled clinical trials may help further guide personalized care for BC immunotherapy.

Recent advances in breast cancer research impacting clinical diagnostic practice

During the last decade, the genomics revolution has driven critical advances in molecular oncology and pathology, and a deeper appreciation of heterogeneity that is beginning to reshape our thinking around diagnostic classification. Recent developments have seen existing classification systems modified and improved where possible, gene-based diagnostics implemented and tumour-immune interactions modulated. We present a detailed discussion of this progress, including advances in the understanding of breast tumour classification, e.g. mixed ductal-lobular tumours and the spectrum of triple-negative breast cancer. The latest information on clinical trials and the implementation of gene-based diagnostics, including MammaPrint and Oncotype Dx and others, is synthesised, and emerging targeted therapies, as well as the burgeoning immuno-oncology field, and their relevance in breast cancer, are discussed. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.