The prevalence and clinical relevance of tumor-infiltrating lymphocytes (TILs) in ductal carcinoma in situ of the breast

Background: Tumor-infiltrating lymphocytes (TILs) are a robust prognostic adjunct in invasive breast cancer, but their clinical role in ductal carcinoma in situ (DCIS) has not been ascertained. Patients and methods: We evaluated the prevalence and clinical relevance of TILs in a well annotated series of 1488 consecutive DCIS women with a median follow-up of 8.2 years. Detailed criteria for TILs evaluation were pre-defined involving the International Immuno-Oncology Biomarker Working Group. TILs percentage was considered both as a continuous and categorical variable. Levels of TILs were examined for their associations with ipsilateral breast event (IBE), whether in situ or invasive. Results: Of the 1488 patients with DCIS under study, 35.1% had < 1%, 58.3% 1-49% and 6.5% ≥ 50% peri-ductal stromal lymphocytes. The interobserver agreement in TILs evaluation, measured by the intraclass correlation coefficient (ICC) was 0.96 (95% CI 0.95-0.97). At univariable analysis, clinical factors significantly associated with TILs (P ≥ 0.001) were intrinsic subtype, grade, necrosis, type of surgery. Her-2 positive DCIS were more frequently associated with TILs (24% of patients with TILs ≥ 50%), followed by the triple negative (11%), Luminal B/Her-2 positive (9%) and Luminal A/B subtypes (1%) (P < 0.0001). We did not find any association between TILs as a continuous variable and the risk of IBEs. Likewise, when patients were stratified by TILs percentage (<1%, between 1% and 49.9%, and ≥ 50%), no statistically significant association was observed (10- year cumulative incidence of IBEs: 19%, 17.3%, and 18.7% respectively, P = 0.767). Conclusion: TILs occur more frequently in the Her-2 positive DCIS. Although we did not find a significant association between TILs and the 10-year risk of IBE, our data suggest that immunotherapies might be considered in subsets of DCIS patients.