A growing body of evidence suggests that hormone receptor-positive (HR+)/HER2+ BC and HR-negative (HR−)/HER2+ BC are biologically different, with complex molecular bidirectional crosstalk between the estrogen receptor and HER2 pathway potentially affecting sensitivity to both HER2-targeted and endocrine therapy in patients with HR+/HER2+ BC. The gene discussed is NR4A1; the disease is breast cancer.