Two of the 31 most differentially expressed genes between the ESR1-negative and ESR1-positive BRCA1 tumours, CD133 and MMP7 (Table 1), were evaluated by immunohistochemistry and immunofluorescence in an independent series of 15 BRCA1 tumours, previously classified as basal or luminal (Figure 2). The gene discussed is PROM1; the disease is neoplasm.