Association of Stromal Tumor-Infiltrating Lymphocytes With Recurrence-Free Survival in the N9831 Adjuvant Trial in Patients With Early-Stage HER2-Positive Breast Cancer.

Importance: The presence of tumor-infiltrating lymphocytes at diagnosis is reported to be prognostic in triple-negative breast cancer.

Objective: To evaluate the association of stromal tumor-infiltrating lymphocytes (STILs) with recurrence-free survival (RFS) in women with human epidermal growth factor receptor 2 (HER2)-positive breast cancer treated with chemotherapy or chemotherapy plus trastuzumab in the N9831 trial.

Design, Setting, And Participants: Hematoxylin-eosin-stained tumor slides from patients with early-stage HER2-positive breast cancer in 2 of the 3 arms of the N9831 trial were assessed for STILs at an academic medical center.