Luminal (ER+) breast tumours were sampled before and after neoadjuvant HT; specifically aromatase inhibition (letrozole) and the expression of CD133 mRNA (a marker for CSCs) increased (P<0.04; Wald's test) as ER mRNA levels decreased (P<0.007; Wald's test) in the post-aromatase inhibition tumour samples (Fig. 1a, GSE10281)14. Here, ESR1 is linked to neoplasm.