Thus the critical question is do these five molecular portraits represent cell types in normal tissue?  If there are extensive similarities between the portraits and cell types in normal tissue, this would suggest that tumours arise from specific cell lineages and their differentiation stages in a manner similar to haematological cancers and that the tumour reflects the biology of non-transformed precursor.  If however the portraits do not represent normal cell types this would suggest that they reflect the long-term accumulation of mutations in pathways from a rare cell and that it is these mutations that drive the phenotype. We are therefore building an atlas of protein expression in all of these five portraits using cell lines that are representative of each type and comparing these to expression profiles in tumours of each type and stage.