Recently published data show discrepancies between P53 cDNA and DNA sequencing results in glioblastoma, colorectal cancer and pleomorphic xanthoastrocytoma. We hypothesized that similar discrepancies are observed in other types of human cancers. Using DNA and cDNA direct sequencing, we analyzed 40 cases of invasive breast duct carcinoma, 23 cases of acute myeloblastic leukaemia, 12 cases of astrocytoma and 40 cases of soft tissue sarcoma for P53 mutations. Additionally, we used real-time quantitative PCR to estimate the normalized relative P53 expression. In the comparative study, the P53 mutation was detected more frequently when using cDNA sequencing than DNA sequencing in all of the cancer types. Furthermore, several samples presented missense P53 mutations, with visible wild-type nucleotide on the DNA sequence. In contrast, elimination of the wild-type allele or selective overproduction of the mutated allele was observed on the cDNA sequence. P53 expression was not significantly different between the cases with or without P53 mutations. These results indicate that cDNA sequencing improves the detection of P53 mutations in these cancers. We suggest that the true incidence of P53 mutations in these cancers is underestimated at the DNA level, and evaluation of the alteration should be carried out using cDNA analysis.