Tumor-infiltrating lymphocytes in breast cancer: Evaluating interobserver variability, heterogeneity, and fidelity of scoring core biopsies

Objectives: The aims were to evaluate breast cancer (BC) tumor-infiltrating lymphocytes (TILs) interobserver variability, heterogeneity, and the fidelity of scoring TILs in core needle biopsy (CNB). Methods: Matching CNB and two full-face sections (FFSs) of BC cases (n = 100) were independently reviewed by two pathologists. Percentage of stromal lymphocytes (TIL-str) and intratumoral lymphocytes (iTu-Ly) were recorded. Results: The weighted ê values for the degree of agreement between both raters were 0.53 to 0.71. However, there was a slight improvement in the interobserver variability for TIL-str and slight decline in iTu-Ly when ER+/HER2-cases were excluded. The intraclass correlation coefficient for FFS1 vs FFS2 was 0.91 for TIL-str and 0.96 for iTu-Ly. Spearman correlation coefficient for CNB vs FFS1/FFS2 was 0.81 for TIL-str and 0.79 for iTu-Ly. Conclusions: We conclude that the agreement in TILs scoring between the raters is acceptable. Caution should be practiced when scoring iTu-Ly in CNBs.