NTN1 and neoplasm: Based on the screen for netrin-1 expression in human tumour cell lines, we noticed that while a fraction of cell lines express netrin-1 and undergo apoptosis upon netrin-1 silencing [Fig 1A and (Delloye-Bourgeois et al, 2009a)], other cell lines failed to show netrin-1 expression and are resistant to netrin-1 interference (Fig 1A).