Prognostic and Predictive Significance of Stromal Tumor-Infiltrating Lymphocytes (sTILs) in ER-Positive/HER2−Negative Postmenopausal Breast Cancer Patients

SIMPLE SUMMARY: The presence of immune cells within the tumor (TILs) indicates good prognosis for some aggressive breast cancer subtypes. However, less is known about TILs role within the hormone-responsive breast cancer (ER+/HER2−). These tumors represent up to 70% of all breast cancers and often exhibit long-term metastasis. TILs were quantified in tumor section samples from 763 postmenopausal women who received tamoxifen vs. no treatment and categorized into low, intermediate, or high. Among the ER+/HER2−, TILs were associated with poor prognostic variables but did not have prognostic value. High TILs indicate less benefit from tamoxifen. Interestingly, high gene expression of some TIL markers did indicate good prognosis even after adjusting for other clinical variables or were associated with less tamoxifen benefit. These results suggest that TIL markers could be used as prognostic, predictive indicators, and potential candidates for immunotherapy interventions after tamoxifen failure. ABSTRACT: The clinical impact of tumor-infiltrating lymphocytes (TILs) is less known for breast cancer patients with the estrogen receptor-positive (ER+)/human epidermal growth factor receptor-negative (HER−) subtype. Here, we explored the prognostic and predictive value of TILs regarding distant recurrence-free interval (DRFI) and breast cancer-specific survival (BCSS) in 763 postmenopausal patients randomized to receive tamoxifen vs. no systemic treatment. TILs were assessed in whole section tumor samples stained with H&E and divided into low (<10%), intermediate (10–39%), or high (≥40%). High TILs were associated with poor prognostic variables and good prognoses for all patients, but not within the ER+/HER2− group. Within the ER+/HER2− group, high gene expression of CD19 and PD-L1 and high IMMUNE1 score indicated good prognosis in multivariable analysis while high CD8 and CD19 gene expression and high IMMUNE1 score were associated with less tamoxifen benefit. These results indicate that within the ER+/HER2− subtype there could be subsets of patients where expression of specific TIL markers might be used to reveal candidates for immune therapy interventions upon failure of the endocrine therapy.