HR and breast cancer: Parkes et al. analyzed 1,048 BC patients with bone-only metastasis as the first site of metastasis at MD Anderson Cancer Center and also found that HR+/HER2− subtype contributed to the majority (78%), followed by 11% in HR+/HER2+, 7% in HR−/HER2− and 3% in HR−/HER2+ [12].