In agreement with the importance of the SH2 phosphotyrosine binding site of Grb7 in Grb7-mediated signal transduction cascades and cancer malignancy, the specific Grb7 peptide targeting the SH2 phosphotyrosine binding site of Grb7 efficiently blocks Grb7-mediated signal transduction cascades. The gene discussed is GRB7; the disease is cancer.