Tumor-Infiltrating Lymphocytes in Triple-Negative Breast Cancer

Key PointsQuestionIn patients with early-stage triple-negative breast cancer (TNBC) treated with locoregional therapy but without adjuvant or neoadjuvant chemotherapy, is a higher abundance of tumor-infiltrating lymphocytes (TIL) in breast cancer tissue associated with better survival? FindingsIn this retrospective analysis of 1966 participants with early-stage TNBC treated with locoregional therapy but without adjuvant or neoadjuvant chemotherapy, survival rates were 90% for patients with a TIL level of 50% or greater, compared with 72% for patients with a TIL level of less than 30% at 5-year follow-up. MeaningIn patients with early-stage TNBC treated with locoregional therapy only, higher TIL levels in breast cancer tissue were associated with improved survival. ImportanceThe association of tumor-infiltrating lymphocyte (TIL) abundance in breast cancer tissue with cancer recurrence and death in patients with early-stage triple-negative breast cancer (TNBC) who are not treated with adjuvant or neoadjuvant chemotherapy is unclear. ObjectiveTo study the association of TIL abundance in breast cancer tissue with survival among patients with early-stage TNBC who were treated with locoregional therapy but no chemotherapy. Design, Setting, and ParticipantsRetrospective pooled analysis of individual patient-level data from 13 participating centers in North America (Rochester, Minnesota; Vancouver, British Columbia, Canada), Europe (Paris, Lyon, and Villejuif, France; Amsterdam and Rotterdam, the Netherlands; Milan, Padova, and Genova, Italy; Gothenburg, Sweden), and Asia (Tokyo, Japan; Seoul, Korea), including 1966 participants diagnosed with TNBC between 1979 and 2017 (with follow-up until September 27, 2021) who received treatment with surgery with or without radiotherapy but no adjuvant or neoadjuvant chemotherapy. ExposureTIL abundance in breast tissue from resected primary tumors. Main Outcomes and MeasuresThe primary outcome was invasive disease-free survival [iDFS]. Secondary outcomes were recurrence-free survival [RFS], survival free of distant recurrence [distant RFS, DRFS], and overall survival. Associations were assessed using a multivariable Cox model stratified by participating center. ResultsThis study included 1966 patients with TNBC (median age, 56 years [IQR, 39-71]; 55% had stage I TNBC). The median TIL level was 15% (IQR, 5%-40%). Four-hundred seventeen (21%) had a TIL level of 50% or more (median age, 41 years [IQR, 36-63]), and 1300 (66%) had a TIL level of less than 30% (median age, 59 years [IQR, 41-72]). Five-year DRFS for stage I TNBC was 94% (95% CI, 91%-96%) for patients with a TIL level of 50% or more, compared with 78% (95% CI, 75%-80%) for those with a TIL level of less than 30%; 5-year overall survival was 95% (95% CI, 92%-97%) for patients with a TIL level of 50% or more, compared with 82% (95% CI, 79%-84%) for those with a TIL level of less than 30%. At a median follow-up of 18 years, and after adjusting for age, tumor size, nodal status, histological grade, and receipt of radiotherapy, each 10% higher TIL increment was associated independently with improved iDFS (hazard ratio [HR], 0.92 [0.89-0.94]), RFS (HR, 0.90 [0.87-0.92]), DRFS (HR, 0.87 [0.84-0.90]), and overall survival (0.88 [0.85-0.91]) (likelihood ratio test, P<10e-6). Conclusions and RelevanceIn patients with early-stage TNBC who did not undergo adjuvant or neoadjuvant chemotherapy, breast cancer tissue with a higher abundance of TIL levels was associated with significantly better survival. These results suggest that breast tissue TIL abundance is a prognostic factor for patients with early-stage TNBC. This study of patients with early-stage triple-negative breast cancer not treated with adjuvant or neoadjuvant chemotherapy analyzes the association between tumor-infiltrating lymphocyte levels, cancer recurrence, and survival.