Conclusions
Abundant TILs are an independent prognostic factor in HR-/HER2+ breast cancers. Evaluation of TILs in HR-/HER2+ breast cancers may provide valuable information regarding the prognosis of patients treated using adjuvant chemotherapy and trastuzumab.
Methods
We retrospectively evaluated the relationship of TILs and TLS and the expression of MHC I in 447 HER2-positive breast cancers treated with chemotherapy and 1 year of trastuzumab.
Results
TILs were more abundant in hormone receptor (HR)-/HER2+ tumors than in HR+/HER2+ tumors. HR-/HER2+ breast cancers with abundant TILs showed a higher histologic grade, the absence of lymphovascular invasion, the presence of peritumoral lymphocytic infiltration, moderate to abundant TLSs in adjacent tissue, and stronger HLA-ABC and HLA-A expression. Abundant TILs and the absence of lymphovascular invasion were found to be good, independent prognostic factors for disease-free survival in patients with HR-/HER2+ breast cancer. The level of TILs was not associated with the patients' prognosis in HR+ tumors. Conclusions: Abundant TILs are an independent prognostic factor in HR-/HER2+ breast cancers. Evaluation of TILs in HR-/HER2+ breast cancers may provide valuable information regarding the prognosis of patients treated using adjuvant chemotherapy and trastuzumab.