For example, the Cancer and Leukemia Group B (CALGB) 9343 randomized controlled trial showed that the 5‐year recurrence rates were very low (4% without RT vs. 1% with RT, p < 0.001)8 regardless of receipt of RT after BCS, in women over 70 and diagnosed with low‐risk (i.e., early‐stage, node‐negative, and estrogen receptor [ER]‐positive) breast cancer (LRBC). Here, ESR1 is linked to breast cancer.