Histopathological Assessment of Tumor-Infiltrating Lymphocytes

Histopathological assessment of predictive factors was made for core needle biopsy (CNB) specimens for primary lesions at the time of the breast cancer diagnosis. Histopathologic analysis of the percentage of TILs was evaluated on a single full-face hematoxylin and eosin (HE)-stained tumor section using criteria described by Salgado et al [19 (link)]. TILs were defined as the infiltrating lymphocytes within tumor stroma and were expressed in proportion to the field investigated [19 (link)–21 (link)]. The area of in situ carcinoma and crush artifacts were not included. Proportional scores were defined as 3, 2, 1, and 0 if the area of stroma with lymphoplasmacytic infiltration around invasive tumor cell nests was > 50%, > 10–50%, ≤ 10%, and absent, respectively (Fig 1). TILs were considered positive when scores were ≥ 2, and negative when scores were 1 and 0. Histopathologic evaluation of TILs was jointly performed by two breast pathologists, who were blinded to clinical information, including treatment allocation and outcomes.