ESR1 and neoplasm: The previous observation that OPN expression seems to be associated with the increased appearance of predominantly triple-negative tumours (Rudland et al, 2002; Cook et al, 2005; McAllister et al, 2008) appears to be reflected by our results showing that ER- and HER2-negative tumours predominantly express high OPN levels (see Figure 2A, cluster II and Figure 2D).