Nuclear p53 phosphoprotein regulates normal cell proliferation, and accumulation of non-functional mutated p53 in tumor cell nuclei is associated with the development and/or progression of several neoplastic diseases, including breast cancer [12]. Activation of p53 induces senescence and cell-cycle arrest under excessive oncogenic stress and this is a crucial mechanism regulating the inhibition of tumorigenesis. The gene discussed is TP53; the disease is neoplasm.