IGFBP3 and carcinoma: Among the components of this signaling cascade, TβR‐V and PP2A have been proved to be tumor suppressor genes by that stable transfection of human carcinoma cells and CHO‐LRP‐1−/− cells with LRP‐1 (TβR‐V) cDNA restores the growth inhibitory response to IGFBP‐3 and TGF‐β, and normal epithelial morphology10, 15 and by that loss of PP2A regulatory subunit B56δ promotes spontaneous tumorigenesis in vivo.46