In the discovery cohort, low nuclear DARPP-32 expression was significantly associated with increased pleomorphism (χ2 = 6.943, d.f. = 2, P = 0.031), ER and PgR positive tumours (χ2 = 51.128, d.f. = 1, P < 0.001 and χ2 = 22.736, d.f. = 1, P < 0.001 respectively), HER2 negative tumours (χ2 = 13.790, d.f. = 1, P < 0.001), and the absence of triple negative disease (χ2 = 16.472, d.f. = 1, P < 0.001) (Table 1). This evidence concerns the gene PPP1R1B and neoplasm.