ESR1 and breast cancer: In this study, pCR was significantly higher for patients with HER2-negative (IHC 0) vs HER2-low tumors (OR 1.73, P = .036).35 A recent study examined immune-related gene signatures in HER2-negative BC (TNBC) patients treated with immune checkpoint inhibitors.36 It found that tumors with ER levels of 1%-9% and 10%-50% had similar levels of stromal TILs, CD8+ T cells, and PD-L1 positivity to ER 0% tumors, but higher levels than those with ER ≥51%.