Result from mutations: although mutations occur randomly through our dna, a small subset of mutations can cause cancer. Mutations can either make a protein function abnormally, or destroy function; both affects contribute to cancer. Mutations in genes coding for two classes of proteins can cause cancer: proteins whose normal function = regulate cell division, tumor suppressors: their protein products normally guard against cancer. Signal transduction cascades: most cells in the body are not dividing = remain in g0, however, we need to have a way of getting cells to divide when needed. Recall pdgf actions when getting a cut. Pdgfr: proteins with sh2 domains now bind pdgfr and become activated. We"ll follow one of these proteins: after binding pdgfr and becoming activated, this protein in turn binds to another protein, activating it. This protein then binds to and activates another protein, and so on.