LAUSR

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.