ERBB2 and neoplasm: Despite the complexity of the immune system and intricate interplay between tumor and host antitumor immunity, detection of stromal tumor-infiltrating lymphocytes (sTILs), as quantified by visual assessment on routine hematoxylin and eosin (H&E)-stained slides, has emerged as a robust prognostic and predictive biomarker in triple-negative and HER2-positive breast cancer1–3.