ESR1 and neoplasm: Interestingly, 10 tumor pairs switched tumor marker status in the transition from PT to IBTR (ER: n = 1; PgR: n = 6; Ki-67: n = 7), which were in most cases validated by proteogenomics (RNA level: ER n = 1/1, PgR n = 4/6, Ki-67 n = 1/7; protein level: PgR n = 4/6, Ki-67 n = 1/7; Supplementary Fig. 1a, b).