The evaluation of tumor-infiltrating lymphocytes (TILs) in breast cancer: recommendations by an International TILs Working Group 2014

Abstract

Background: The morphological evaluation of tumor-infiltrating lymphocytes (TILs) in breast cancer (BC) is gaining momentum as evidence strengthens for the clinical relevance of this immunological biomarker. Accumulating evidence suggests that the extent of lymphocytic infiltration in tumor tissue can be assessed as a major parameter by evaluation of hematoxylin and eosin (H&E)-stained tumor sections. TILs have been shown to provide prognostic and potentially predictive value, particularly in triple-negative and human epidermal growth factor receptor 2-overexpressing BC.

Design: A standardized methodology for evaluating TILs is now needed as a prerequisite for integrating this parameter in standard histopathological practice, in a research setting as well as in clinical trials. This article reviews current data on the clinical validity and utility of TILs in BC in an effort to foster better knowledge and insight in this rapidly evolving field, and to develop a standardized methodology for visual assessment on H&E sections, acknowledging the future potential of molecular/multiplexed approaches.

Conclusions: The methodology provided is sufficiently detailed to offer a uniformly applied, pragmatic starting point and improve consistency and reproducibility in the measurement of TILs for future studies.

Keywords: breast cancer (BC); clinical validity; prediction; prognosis; tumor-infiltrating lymphocytes (TILs).

Figure 1.

The cellular cross-talk between different leukocyte subsets and their predominant contribution to either pro- or antitumor activities, including myeloid lineage leukocytes, tumor-associated macrophages with either protumorigenic (M2) or antitumorigenic (M1) properties, helper T-cell subsets, cytotoxic T cells, regulatory T cells, B cells, dendritic cells and myeloid-derived suppressor cells are shown. These cells play central roles in shaping the microenvironment via the factors they produce thereby driving either an immune-mediated anti- or protumor activities in the microenvironment.

Figure 2.

Morphology, definitions, biological and diagnostic relevance of the different immune infiltrates found in breast cancer.

Figure 3.

Standardized approach for TILs evaluation in breast cancer.

Figure 4.

Standardization and guidelines for TILs assessment. Stromal TILs should be reported as a percentage (the schematic images might provide some guidance). If the percentage of TILs is questionable, discuss the case with a second pathologist. In heterogenous tumors, evaluate different regions and report the average. For this standardized graphic, images were selected that are representative of different TILs levels, based on the results of three pathologists as well as image analysis. The stromal area was marked in each image. The central images are digitally generated graphics showing the same region of interest (ROI) and a similar density of TILs as the corresponding histological image. Please note that the central images contain idealized TILs generated graphically with comparably density, but not with the exact configuration and distribution as the TILs in the histological images.