For example, Savas et al. studied tumor evolution in 3 estrogen-receptor (ER)-positive, human epidermal growth factor receptor 2 (HER2)-negative breast cancer patients, and 1 triple-negative breast cancer patient, using primary tumor and 5–12 matched metastatic samples from the CASCADE program [8]; and Hoadley et al. profiled primary tumors with 4–5 matched metastases genomically and transcriptomically in 2 triple-negative breast cancer patients [7]. Here, ESR1 is linked to breast cancer.