Tumor Infiltrating Lymphocytes (TILS) and PD-L1 Expression in Breast Cancer: A Review of Current Evidence and Prognostic Implications from Pathologist's Perspective

With the rise of novel immunotherapies able to stimulate the antitumor immune response, increasing literature concerning the immunogenicity of breast cancer has been published in recent years. Numerous clinical studies have been conducted in order to identify novel biomarkers that could reflect the immunogenicity of BC and predict response to immunotherapy. In this regard, TILs have emerged as an important immunological biomarker related to the antitumor immune response in BC. TILs are more frequently observed in triple-negative breast cancer and HER2+ subtypes, where increased TIL levels have been linked to a better response to neoadjuvant chemotherapy and improved survival. PD-L1 is a type 1 transmembrane protein ligand expressed on T lymphocytes, B lymphocytes, and antigen-presenting cells and is considered a key inhibitory checkpoint involved in cancer immune regulation. PD-L1 immunohistochemical expression in breast cancer is observed in about 10-30% of cases and is extremely variable based on tumor stage and molecular subtypes. Briefly, TNBC shows the highest percentage of PD-L1 positivity, followed by HER2+ tumors. On the other hand, PD-L1 is rarely expressed (0-10% of cases) in hormone-receptor-positive BC. The prognostic role of PD-L1 expression in BC is still controversial since different immunohistochemistry (IHC) clones, cut-off points, and scoring systems have been utilized across published studies. In the present paper, an extensive review of the current knowledge of the immune landscape of BC is provided. TILS and PD-L1 expression across different BC subtypes are discussed, providing a guide for their pathological assessment and reporting.

Review of the status of neoadjuvant therapy in HER2-positive breast cancer

Purpose

The development of human epidermal growth factor receptor 2 (HER2)-directed therapies has revolutionized the treatment of HER2-positive breast cancer. The aim of this article is to review the continually evolving treatment strategies in the neoadjuvant setting of HER2-positive breast cancer, as well as the current challenges and future perspectives.

Methods

Searches were undertaken on PubMed and Clinicaltrials.gov for relevant publications and trials.

Findings

The current standard of care in high-risk HER2-positive breast cancer is to combine chemotherapy with dual anti-HER2 therapy, for a synergistic anti-tumor effect. We discuss the pivotal trials which led to the adoption of this approach, as well as the benefit of these neoadjuvant strategies for guiding appropriate adjuvant therapy. De-escalation strategies are currently being investigated to avoid over treatment, and aim to safely reduce chemotherapy, while optimizing HER2-targeted therapies. The development and validation of a reliable biomarker is essential to enable these de-escalation strategies and personalization of treatment. In addition, promising novel therapies are currently being explored to further improve outcomes in HER2-positive breast cancer.

Tumor Infiltrating Lymphocytes across Breast Cancer Subtypes: Current Issues for Biomarker Assessment

Tumor-infiltrating lymphocytes (TILs) represent a surrogate biomarker of anti-tumor, lymphocyte-mediated immunity. In early, triple-negative breast cancer, TILs have level 1B of evidence to predict clinical outcomes. TILs represent a promising biomarker to select patients who can experience a better prognosis with de-intensified cancer treatments and derive larger benefits from immune checkpoint inhibitors. However, the assessment and the validation of TILs as a biomarker require a prospective and rigorous demonstration of its clinical validity and utility, provided reproducible analytical performance. With pending data about the prospective validation of TILs' clinical validity to modulate treatments in early breast cancer, this review summarizes the most important current issues and future challenges related to the implementation of TILs assessments across all breast cancer subtypes and their potential integration into clinical practice.

Systemic Therapy for HER2-Positive Metastatic Breast Cancer: Moving Into a New Era

Patients with HER2-positive breast cancer account for approximately 15% to 20% of all breast cancers and represent one of the most aggressive breast cancer subtypes. Survival rates of patients with metastatic disease have improved dramatically and progressively. Many new agents have been developed, and long-term follow-up from trials of anti-HER2 agents has shown long-term responses. The availability of novel, highly active anti-HER2 treatments, together with the ongoing development of promising diagnostic tools, will offer the unprecedented opportunity to raise cure rates. Our ultimate goal is to tailor treatment intensity to disease and patient characteristics, hopefully increasing the fraction of cured patients while minimizing the risk for overtreatment. If conducted rationally and carefully, this plan has the potential to break a decades-long paradigm, leading to a new, precise era of treatment of HER2-positive breast cancer.

Beta-2 Adrenergic Receptor Gene Expression in HER2-Positive Early-Stage Breast Cancer Patients: A Post-hoc Analysis of the NCCTG-N9831 (Alliance) Trial

BACKGROUND

Beta-2 adrenergic receptor (ß2AR) modulates immune activation and may enhance trastuzumab activity. We assessed the impact of ß2AR gene (ADRB2) expression on the outcomes of patients with HER2-positive early-stage breast cancer enrolled on the NCCTG-N9831 trial.

PATIENTS AND METHODS

This is a post-hoc analysis of the NCCTG-N9831 trial, which compared chemotherapy (arm A) versus chemotherapy plus trastuzumab (arms B&C) as adjuvant treatment of patients with HER2-positive early-stage breast cancer, with disease-free survival (DFS) as primary endpoint. Gene expression levels retrieved by DASL assay were used to classify patients as ADRB2-high or ADRB2-low. Hazard ratios (HRs) were calculated by a Cox proportional model adjusted for prognostic variables and ADRB2 expression. Correlations between ADRB2 expression and stromal tumor-infiltrating lymphocyte (TIL) levels were assessed with Pearson coefficient. A multivariable Cox regression model with interaction term was performed to assess the interaction between ADRB2 expression and treatment arm; and ADRB2 expression and a 8-gene signature previously shown to predict trastuzumab benefit.

RESULTS

Overall, 1,282 patients were included (ADRB2-high [N = 944] / ADRB2-low [N = 338]). A high expression of ADRB2 was associated with a longer DFS (P = .01) in the overall population. The addition of trastuzumab to chemotherapy improved DFS only in patients with ADRB2-high tumors (P < .01). ADRB2 expression was correlated with TIL levels (r = 0.24, P < .001). No association between ADRB2 expression and the 8-gene trastuzumab benefit signature was observed (P = .32).

CONCLUSION

Our findings suggest that a high ADRB2 expression is a favorable prognostic factor and may identify patients with HER2-positive early-stage breast cancer who benefit from adjuvant trastuzumab.

TRIAL REGISTRATION

clinicaltrials.gov NCT00005970.

Aiming at a Tailored Cure for ERBB2-Positive Metastatic Breast Cancer: A Review

Importance

Metastatic breast cancer (MBC) has traditionally been considered incurable. Accordingly, current treatment algorithms are aimed at maintaining quality of life and improving overall survival, rather than at complete eradication of the disease. Attempts to achieve cure with high-dose chemotherapy were conducted in the 1990s, with no observed long-term benefit compared with conventional chemotherapy. Nonetheless, Erb-B2 receptor tyrosine kinase 2 (ERBB2, formerly HER2)-targeted biologic treatments, developed in the past 2 decades, are currently challenging this paradigm. Indeed, a fraction of patients with ERBB2-positive MBC achieve long-lasting responses to chemotherapy and ERBB2-blockade, resembling a cure. In this setting, the challenge of identifying the optimal curable population has emerged, including identifying populations in whom treatment escalation strategies may be beneficial, while avoiding overtreatment in patients with incurable disease.

Observations

A number of clinical and pathologic features allow physicians to identify patients with ERBB2-positive MBC who are more likely to experience a long-lasting response to chemotherapy and ERBB2-blockade. Long-term responders tend to be de novo metastatic, have a reduced disease burden, and tend to show deep responses to systemic treatment. In pathologic terms, features associated with long-term response are high ERBB2 expression, lack of detrimental genomic aberrations, and antitumor immune activation. This population of patients may potentially derive benefit from a tailored escalation of frontline treatment with novel anti-ERBB2 drugs, such as trastuzumab deruxtecan, tucatinib, or margetuximab. Additional recent therapeutic and diagnostic advancements could further aid in the path toward a cure for ERBB2-positive MBC.

Conclusions and Relevance

Careful implementation of novel diagnostic and treatment tools could potentially expand the population of patients with ERBB2-positive MBC experiencing long-lasting disease response. Trials are in preparation to confirm this paradigm, and hopefully lead to a new era of precision therapy for breast cancer.