Intra-Tumour Heterogeneity Is One of the Main Sources of Inter-Observer Variation in Scoring Stromal Tumour Infiltrating Lymphocytes in Triple Negative Breast Cancer.

Darren Kilmartin,Sharon A Glynn,Grace Callagy,Elisabeth Specht Stovgaard,Päivi Heikkilä,Vasiliki Zolota,Cecily Quinn,Inta Liepniece-Karele,Zsuzsanna Bagó-Horváth,Elena Provenzano,Angelika Reiner,Mark O’Loughlin,Giuseppe Floris,Xavier Andreu,Caterina Marchiò,Aleš Ryška,Ewa Chmielik,Mark Webber,Anikó Kovács,Gábor Cserni,Davood Roshan,Simonetta Bianchi,Maria Pia Foschini,Anna Sapino,Paulo Figueiredo,Peter Regitnig,Janina Kulka,Anne‐Vibeke Lænkholm

doi:10.3390/cancers13174410

Abstract

Simple SummaryThe stromal tumour infiltrating lymphocytes (sTILs) within a tumour are a strong predictor of outcome for patients with triple negative breast cancer (TNBC). However, the assessment of sTILs is subject to variation and needs to be standardized in order for it to be used more widely as a biomarker. The aim of this study was to determine the level of consistency that can be achieved when an internet-based scoring aid is used to assist with evaluation of sTILs. Twenty-three breast pathologists across Europe scored sTILs in 49 cases of TNBC taken from a routine diagnostic practice using this aid. The consistency of scoring sTILs was good. However, variation in the distribution of sTILs within the tumour resulted in discordance between pathologists scoring cases, particularly as it caused variability in the selection of regions of the tumour to score. More rigorous training of pathologists is needed for standardization of sTILs assessment, which may potentially be improved using automated approaches. Stromal tumour infiltrating lymphocytes (sTILs) are a strong prognostic marker in triple negative breast cancer (TNBC). Consistency scoring sTILs is good and was excellent when an internet-based scoring aid developed by the TIL-WG was used to score cases in a reproducibility study. This study aimed to evaluate the reproducibility of sTILs assessment using this scoring aid in cases from routine practice and to explore the potential of the tool to overcome variability in scoring. Twenty-three breast pathologists scored sTILs in digitized slides of 49 TNBC biopsies using the scoring aid. Subsequently, fields of view (FOV) from each case were selected by one pathologist and scored by the group using the tool. Inter-observer agreement was good for absolute sTILs (ICC 0.634, 95% CI 0.539–0.735, p < 0.001) but was poor to fair using binary cutpoints. sTILs heterogeneity was the main contributor to disagreement. When pathologists scored the same FOV from each case, inter-observer agreement was excellent for absolute sTILs (ICC 0.798, 95% CI 0.727–0.864, p < 0.001) and good for the 20% (ICC 0.657, 95% CI 0.561–0.756, p < 0.001) and 40% (ICC 0.644, 95% CI 0.546–0.745, p < 0.001) cutpoints. However, there was a wide range of scores for many cases. Reproducibility scoring sTILs is good when the scoring aid is used. Heterogeneity is the main contributor to variance and will need to be overcome for analytic validity to be achieved.

Highlights

Stromal tumour infiltrating lymphocytes have emerged as a strong prognostic factor in HER2 positive and triple negative breast cancer (TNBC) [1]
Inter-observer agreement between the 23 pathologists for the absolute sTILs score for the 49 cases was good (ICC 0.634, 95% CI 0.539–0.735, p < 0.001)
Reports of reproducibility scoring sTILs emanated from studies that were designed to assess prognostic significance, mainly in TNBC and HER2 positive BC taken from clinical trials [2,3,4,5,6,7,8,9,23]

Summary

Introduction

Stromal tumour infiltrating lymphocytes (sTILs) have emerged as a strong prognostic factor in HER2 positive and triple negative breast cancer (TNBC) [1]. Guidance for assessing sTILs was produced by the international TIL Working Group (WG), which is known as the International Immuno-Oncology Biomarker-WG [12], and this guidance is recommended by the WHO as the methodology for quantifying sTILs in BC [13]. It advises that sTILs are assessed in treatment naive tumours, within the tumour boundary and as a continuous variable. The website includes an interactive scoring aid and a prognostic tool for TNBC into which the absolute sTILs value is incorporated in current practice, sTILs assessment is used for stratifying cases in clinical trials and in studies evaluating prognosis, and while assessment of sTILs is included in the pathology report in some centres, it is not yet included in minimum datasets for BC reporting

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