Targeting proteins for proteasomal degradation using the PROTAC approach is now widely pursued in clinical development, mainly targeting proteins in cancer (e.g., BCR–ABL,362, 363 EGFR,361, 364, 365 androgen receptor (AR),366, 367, 368 estrogen receptor (ER),369, 370 bromodomain‐containing protein 4 (BRD4),371 or Bruton's kinase (BTK)372, 373). Here, ESR1 is linked to cancer.