The journey of tumor-infiltrating lymphocytes as a biomarker in breast cancer: clinical utility in an era of checkpoint inhibition.

In 2014, we described a method to quantify percentage of tumor-infiltrating lymphocytes (TILs) on hematoxylin and eosin-stained slides of breast cancer samples using light microscopy that could be performed easily by pathologists with no extra stains. The aim of detailing the method was to facilitate independent research groups replicating our prognostic findings using TIL quantity in early-stage breast cancers. A global working group of breast pathologists was convened to standardize, test reproducibility, and refine the method. A website was also established which allowed free training (www.tilsinbreastcancer.org). As a result of this work, TIL data have been collected in over 20 000 primary breast cancer samples worldwide and the robust associations with better prognoses in triple-negative breast cancer (TNBC) and HER2+ BC have been confirmed. This has resulted in the inclusion of the TIL biomarker in several international breast cancer guidelines as well as in national criteria for routine pathology reporting. TIL therefore represents the first biological prognostic biomarker for early-stage TNBCs, and here its prognostic effect is linear, with values of 30%-50% being suggested as suitable for use in potential chemotherapy de-escalation studies. The efficacy of immune checkpoint-targeted agents in breast cancer now provides direct evidence that host immune responses can modify tumor growth in some patients. With the recent granting of accelerated approvals for the first PD-1/PD-L1 targeting agents in early and advanced TNBC, our focus has now moved to investigating the clinical utility of TIL in the setting of immune checkpoint agents, with or without PD-L1 protein assessment. Emerging data suggest that TIL quantity can help clinicians identify patients with breast cancer who benefit most from PD-1/PD-L1 inhibition. In patients with advanced TNBC and HER2+ disease a TIL cut-off of 5% or 10%, with PD-L1 expression can define 'immune-enriched' tumors and currently seems to have the most clinical relevance in this context.

Loi S ，Michiels S ，Adams S ，Loibl S ，Budczies J ，Denkert C ，Salgado R ... -  《-》

Targeting immune pathways in breast cancer: review of the prognostic utility of TILs in early stage triple negative breast cancer (TNBC).

Breast cancer has been one of the last tumor types to see benefit from immunotherapies. Yet, immune infiltrates have been noticed for decades in primary breast cancers. Lately, quantity of tumor infiltrating lymphocytes (TILs) have been reported to have strong prognostic value in improving estimates of distant recurrence-free survival, disease-free and overall survival in early-stage triple negative BC (TNBC) treated with standard adjuvant/neoadjuvant chemotherapy (Level 1B evidence). Quantity, as a percentage of tumor stromal infiltration, is based on an evaluation by pathologists using light microscopy on H&E stained glass slides (see method at www.tilsinbreastcancer.org) [1,2] at time of diagnosis (pre-treatment and in the residual disease post neoadjuvant chemotherapy). Whilst TILs are currently not used for treatment allocation, this is an active area of investigation. Combination of atezolizumab with nab-paclitaxel in a phase III study has recently seen success in terms of improved progression free and overall survival for the PD-L1 -positive population of metastatic TNBC in the first line/newly relapsed setting [3]. This has led to approval of atezolizumab for use in this setting. However, this population was only 41% of the trial population. Data in advanced breast cancer currently suggest requirement for enrichment of the population for preexisting anti-tumor immunity for benefit to PD(L)1 inhibition. Checkpoint inhibitors are currently being investigated in the early-stage setting in a number of phase II/III trials in TNBC with various different anti- PD-1, PD-L1 and CTLA-4 agents. In this context, we will face issues of the best chemotherapy backbone, the possible detrimental role of steroids and growth factor support, risk of overtreatment, differences between PD-1 and PD-L1 inhibition and if we can use a biomarker to effectively escalate or de-escalate chemotherapy and/or use checkpoint inhibition in this setting.

Blackley EF ，Loi S 《-》

The therapeutic candidate for immune checkpoint inhibitors elucidated by the status of tumor-infiltrating lymphocytes (TILs) and programmed death ligand 1 (PD-L1) expression in triple negative breast cancer (TNBC).

Tomioka N ，Azuma M ，Ikarashi M ，Yamamoto M ，Sato M ，Watanabe KI ，Yamashiro K ，Takahashi M ... -  《-》

The path to a better biomarker: application of a risk management framework for the implementation of PD-L1 and TILs as immuno-oncology biomarkers in breast cancer clinical trials and daily practice.

Immune checkpoint inhibitor therapies targeting PD-1/PD-L1 are now the standard of care in oncology across several hematologic and solid tumor types, including triple negative breast cancer (TNBC). Patients with metastatic or locally advanced TNBC with PD-L1 expression on immune cells occupying ≥1% of tumor area demonstrated survival benefit with the addition of atezolizumab to nab-paclitaxel. However, concerns regarding variability between immunohistochemical PD-L1 assay performance and inter-reader reproducibility have been raised. High tumor-infiltrating lymphocytes (TILs) have also been associated with response to PD-1/PD-L1 inhibitors in patients with breast cancer (BC). TILs can be easily assessed on hematoxylin and eosin-stained slides and have shown reliable inter-reader reproducibility. As an established prognostic factor in early stage TNBC, TILs are soon anticipated to be reported in daily practice in many pathology laboratories worldwide. Because TILs and PD-L1 are parts of an immunological spectrum in BC, we propose the systematic implementation of combined PD-L1 and TIL analyses as a more comprehensive immuno-oncological biomarker for patient selection for PD-1/PD-L1 inhibition-based therapy in patients with BC. Although practical and regulatory considerations differ by jurisdiction, the pathology community has the responsibility to patients to implement assays that lead to optimal patient selection. We propose herewith a risk-management framework that may help mitigate the risks of suboptimal patient selection for immuno-therapeutic approaches in clinical trials and daily practice based on combined TILs/PD-L1 assessment in BC. © 2020 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Gonzalez-Ericsson PI ，Stovgaard ES ，Sua LF ，Reisenbichler E ，Kos Z ，Carter JM ，Michiels S ，Le Quesne J ，Nielsen TO ，Laenkholm AV ，Fox SB ，Adam J ，Bartlett JM ，Rimm DL ，Quinn C ，Peeters D ，Dieci MV ，Vincent-Salomon A ，Cree I ，Hida AI ，Balko JM ，Haynes HR ，Frahm I ，Acosta-Haab G ，Balancin M ，Bellolio E ，Yang W ，Kirtani P ，Sugie T ，Ehinger A ，Castaneda CA ，Kok M ，McArthur H ，Siziopikou K ，Badve S ，Fineberg S ，Gown A ，Viale G ，Schnitt SJ ，Pruneri G ，Penault-Llorca F ，Hewitt S ，Thompson EA ，Allison KH ，Symmans WF ，Bellizzi AM ，Brogi E ，Moore DA ，Larsimont D ，Dillon DA ，Lazar A ，Lien H ，Goetz MP ，Broeckx G ，El Bairi K ，Harbeck N ，Cimino-Mathews A ，Sotiriou C ，Adams S ，Liu SW ，Loibl S ，Chen IC ，Lakhani SR ，Juco JW ，Denkert C ，Blackley EF ，Demaria S ，Leon-Ferre R ，Gluz O ，Zardavas D ，Emancipator K ，Ely S ，Loi S ，Salgado R ，Sanders M ，International Immuno-Oncology Biomarker Working Group ... -  《-》

Molecular Characteristics of Lymphocyte-predominant Triple-negative Breast Cancer.

Tumor-infiltrating lymphocytes (TILs) are considered a prognostic marker for triple-negative breast cancer (TNBC). Immune checkpoint inhibitor (ICI)-based treatments are more effective for tumors with PD-L1-positive TILs, suggesting crucial roles of TILs in the local tumor immunity. However, factors attracting TILs are still largely unknown. Focusing on tumor antigenicity, we examined TNBC samples to identify the characteristics of TIL-high tumors. Nine treatment-naïve TNBCs (TIL-high: five, TIL-low: four) were subjected to next-generation sequencing (NGS). Loss of heterozygosity (LOH) of PTEN was also analyzed. A variety of copy number variations were observed, and no genes differed significantly between TIL-high and -low groups. However, PTEN loss was more frequently observed in the TIL-high group: 60% compared to 25% in TIL-low tumors. NGS correlated well with LOH analysis in identifying PTEN loss. All three tumors with PTEN loss in the TIL-high group showed high PD-L1. All nine samples were microsatellite-stable. Frequent PTEN loss and high expression of PD-L1 in TIL-high TNBC suggest that PTEN mutation may be a biomarker for ICIs.

Sasaki R ，Horimoto Y ，Yanai Y ，Kurisaki-Arakawa A ，Arakawa A ，Nakai K ，Saito M ，Saito T ... -  《-》