With the exploitation of the advantage of the ability of LC-MS/MS to discriminate protein sequences of different species, we semiquantitatively determined tumor cell-derived (i.e., human) and stroma-derived (i.e., mouse) concentrations of annexin A1 using the exponentially modified protein abundance index (emPAI) (23) algorithm (Fig. 6A). This evidence concerns the gene ANXA1 and neoplasm.