TP53 and neoplasm: In contrast, the expression of miR-184 was almost abrogated in the Tp53−/− tumours and the MMTV-Neu tumours, however, miR-184 expression in the C3 SV40 Tag and MMTV-PyMT tumours was comparable to normal mammary epithelial cells suggesting that miR-184 might be specifically silenced in certain breast cancers or that they derive from different cells of origin (Fig. 2a).