9. Mukai H, Shimizu C, Masuda N, Ohtani S, Ohno S, Takahashi M, et al. Palbociclib in combination with letrozole in patients with estrogen receptor-positive, human epidermal growth factor receptor 2-negative advanced breast cancer: PALOMA-2 subgroup analysis of Japanese patients. Int J Clin Oncol. 2019;24:274-87. This evidence concerns the gene ESR1 and breast cancer.