Th2 infiltration is a better predictor of survival than tumor-infiltrating lymphocytes (TILs) in triple-negative breast cancer (TNBC)

Purpose. Triple-negative breast cancers (TNBC) account for 15% of all breast cancers but carry the worst prognosis. Because of their heterogenicity, these tumors are not all prone to targeted therapies. However, due to their high immune infiltration, targeting their immune microenvironment is of tremendous interest and is becoming the standard of care for high-risk early-stage TNBC. Nevertheless, the characterization of this immune infiltrate is often limited to general tumor-infiltrating lymphocytes (TILs) counting, without characterization of lymphocytes subtypes. Thus, we aimed at precisely characterizing these sub-populations and evaluating their prognostic significance. Methods. We selected 91 TNBC tumors for which we had both the TILs count on hematoxylin and eosin (H&E) slides determined by an expert pathologist and the immune microenvironment cell subtypes characterization using flow cytometry (FC). We then compared the prognostic value of immune microenvironment subpopulations vs total TILs count. Results. TNBCs contained a mean of 22.8±25.9% TILs in the tumor surface area, including mainly CD4+ helper T lymphocytes (14.1%), mostly Th2 (11.7%), CD8+ cytotoxic T lymphocytes (11.1%), and myeloid cells (8.4%) including antigen presenting cells (APC). The TILs count was correlated with the abundance of these cellular subpopulations (p≤0.004). TILs percentage was predictive of overall survival (OS) in univariate analysis (p=0.044), high APC infiltration was predictive of relapse-free survival (RFS) in univariate analysis (p≤0.030), and Th2 infiltration was predictive of both RFS and OS in univariate (p=0.009, 0.008 respectively) and multivariate analyses (p=0.002, 0.010 respectively). Conclusion. The characterization of TILs composition is essential to better understand the potential antitumoral functions of these cells, and to strongly improve the associated prognostic and predictive values. We here demonstrate that Th2 subpopulation is associated with a better overall survival in TNBC and could be of use to predict response to the newly used immunotherapies. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This study was funded by grants from Rennes University Hospital (CORECT 2021-UF 8946-03) and association La Vannetaise ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The Ethics Committee Review Board of Centre de lutte contre le Cancer Eugene Marquis gave ethical approval for this work I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes All data produced in the present study are available upon reasonable request to the authors