With this strategy, it has been demonstrated that spleen tyrosine kinase (Syk), a 72-kDa protein tyrosine kinase (RTK) with duel properties of an oncogene and a tumor suppressor in distinctive cell types (known to play a crucial role in adaptive immune receptor signaling, particularly in B cells), used as a target kinase, helped identify direct substrates of Syk specific to B cells and breast cancer cells. This evidence concerns the gene SYK and breast cancer.