below is excerpt from really informative research article re p53 involvement in cancer growth, found here: http://gan.sagepub.com/content/2/4/466.full

"Mutant p53 proteins not only lose their tumor suppressive activities but often gain additional oncogenic functions that endow cells with growth and survival advantages. Interestingly, mutations in the p53 gene were shown to occur at different phases of the multistep process of malignant transformation, thus contributing differentially to tumor initiation, promotion, aggressiveness, and metastasis.

The many roles of p53 as a tumor suppressor include the ability to induce cell cycle arrest, DNA repair, senescence, and apoptosis, to name only a few. ⁶ Indeed, TP53 mutations were reported to occur in almost every type of cancer at rates varying between 10% (e.g., in hematopoietic malignancies ⁷ ) and close to 100% (e.g., in high-grade serous carcinoma of the ovary ⁸ )"