ABSTRACT: Background:Not all breast cancer patients benefit from neoadjuvant or adjuvant therapy, resulting in considerable undertreatment or overtreatment. New insights into the role of tumor-infiltrating immune cells suggest that their composition, as well as their functionality, might serve as a biomarker to enable optimal patient selection for current systemic therapies and upcoming treatment options such as immunotherapy. Methods:We performed several complementary unbiased in silico analyses on gene expression profiles of 7270 unrelated tumor samples of nonmetastatic breast cancer patients with known clinical follow-up. CIBERSORT was used to estimate the fraction of 22 immune cell types to study their relations with pathological complete response (pCR), disease-free survival (DFS), and overall survival (OS). In addition, we used four previously reported immune gene signatures and a CD8+ T-cell exhaustion signature to assess their relationships with breast cancer outcome. Multivariable binary logistic regression and multivariable Cox regression were used to assess the association of immune cell-type fractions and immune signatures with pCR and DFS/OS, respectively. Results:Increased fraction of regulatory T-cells in human epidermal growth factor receptor 2 (HER2)-positive tumors was associated with a lower pCR rate (odds ratio [OR] = 0.15, 95% confidence interval [CI] = 0.03 to 0.69), as well as shorter DFS (hazard ratio [HR] = 3.13, 95% CI?=?1.23 to 7.98) and OS (HR?=?7.69, 95% CI?=?3.43 to 17.23). A higher fraction of M0 macrophages in estrogen receptor (ER)-positive tumors was associated with worse DFS (HR?=?1.66, 95% CI?=?1.18 to 2.33) and, in ER-positive/HER2-negative tumors, with worse OS (HR?=?1.71, 95% CI?=?1.12 to 2.61). Increased fractions of ?? T-cells in all breast cancer patients related to a higher pCR rate (OR?=?1.55, 95% CI?=?1.01 to 2.38), prolonged DFS (HR?=?0.68, 95% CI?=?0.48 to 0.98), and, in HER2-positive tumors, with prolonged OS (HR?=?0.27, 95% CI?=?0.10 to 0.73). A higher fraction of activated mast cells was associated with worse DFS (HR?=?5.85, 95% CI?=?2.20 to 15.54) and OS (HR?=?5.33, 95% CI?=?2.04 to 13.91) in HER2-positive tumors. The composition of relevant immune cell types frequently differed per breast cancer subtype. Furthermore, a high CD8+ T-cell exhaustion signature score was associated with shortened DFS in patients with ER-positive tumors regardless of HER2 status (HR?=?1.80, 95% CI?=?1.07 to 3.04). Conclusions:The main hypothesis generated in our unbiased in silico approach is that a multitude of immune cells are related to treatment response and outcome in breast cancer.
