Tumor-Infiltrating Lymphocytes as a Prognostic Factor in Triple-Negative Breast Cancer

High levels of tumor-infiltrating lymphocytes (TILs) have long been thought to reflect an intact antitumor immune response. Higher TIL levels have been associated with better survival after adjuvant chemotherapy and a higher pathologic complete remission rate after neoadjuvant chemotherapy. Results from small studies have suggested a link between high TIL levels and survival even without systemic therapy. Now, researchers have conducted an international, retrospective, pooled analysis of individual patient-level data for almost 2000 patients (median age, 56) with early-stage, triple-negative breast cancer (TNBC).

Among these patients, 60% had T1 lesions, 87% had node-negative disease, and 55% had stage 1 disease (T1cN0 tumors, 65%). No patients received systemic therapy; 61% underwent breast-conserving surgery and radiation therapy. TIL percentages were assessed in stromal tissue. The median TIL level was 15%; 34% of patients had TIL levels of at least 30%, and 21% had TIL levels of at least 50%. Higher TIL levels were associated with younger age and higher tumor grade. Median follow-up was 18 years.

Analyses were adjusted for age, tumor size and grade, nodal status, and receipt of radiation therapy. Each 10% higher TIL increment was associated with an 8% improvement in disease-free survival at 5 years, 10% improvement in relapse-free survival (RFS), 13% improvement in distant RFS, and 12% improvement in overall survival (OS). For example, among patients with stage 1 TNBC, those with TILs 50% or greater had 5-year RFS and OS of 89% and 95%, respectively, compared with 73% and 82%, respectively, in patients with TIL levels below 30%.