The p53 gene is known to play a central role in cancer. In fact, no human tumor type is devoid of p53 mutations, although differences can be seen in the relative frequencies and patterns of nucleotide substitutions. Our work illustrates these differences, since frequencies of mutations ranged from 15 to 80% and the patterns of mutations were distinctly different in skin cancers compared to breast tumors. Furthermore, it is well established that whenever p53 mutations occur during tumor progression, their appearance greatly affects the natural evolution of cancer. This is confirmed by the correlations found between p53 mutations and the negative outcome of the disease in a number of tumor types.