To determine the potential differential effects of p53 loss-of-function and gain-of-function mutations on tumor phenotype within the context of a single tissue of origin (salivary tumors arising in MMTV-Hras male transgenic mice), we generated cohorts of mice of the following genotypes: MMTV-Hras/p53+/+, MMTV-Hras/p53-/-, and MMTV-Hras/p53R172H/R172H. The gene discussed is TP53; the disease is neoplasm.