ESR1 and cancer: In contrast, ER-negative tumors are more aggressive and tend to metastasize.[12,13] While adjuvant endocrine therapy prolonged the time to recurrence among ER-positive patients,[14–16] patients who received tamoxifen had cumulative recurrence rates that increased from 15% at 5 years to 33% at 15 years and cumulative cancer mortality rates that increased from 8.3% at 5 years to 26% at 15 years.[14]