Alterations of TP53 in Microdissected Transitional Cell Carcinoma of the Human Urinary Bladder: High Frequency of TP53 Accumulation in the Absence of Detected Mutations is Associated with Poor Prognosis

We have used microdissection of paraffin-embedded histological sections and polymerase chain reaction (PCR)-based direct DNA sequencing for 54 transitional cell carcinoma (TCC) of the bladder, to examine critically the association between TP53 nuclear accumulation determined by immunohistochemistry and the presence of TP53 mutations, and to examine their relationship to tumour stage and grade, as well as patient survival. There was a significant association between the presence of TP53-positive nuclei (> 10%) and a higher histological stage and grade (P = 0.0115, P = 0.0151 respectively; Fisher's exact). A significant association between TP53 gene mutations and TP53 nuclear reactivity in more than 10% of tumour cell nuclei was also observed (P = 0.0003; Fisher's exact). Mutations were detected in 18/54 (33%) cases together with the wild-type sequence when analysed from bulk frozen samples, with significant clustering of mutations in exons 7 and 8. The microdissection method distinguished more clearly between heterozygous and/or homozygous alterations of the TP53 tumour-suppressor gene, and clearly showed frequent accumulation of TP53 in the absence of mutations. When microdissecting immunonegative regions from the same paraffin sections, three out of ten samples showed the identical mutations detected in the immunopositive regions. There was a significant association between TP53 immunoreactivity in more than 50% of tumour cell nuclei and decreased survival among all patients (P = 0.0325; log-rank test). The patients with TP53 mutations showed a trend for a shorter survival period; however, the association was not statistically significant at the 95% confidence level (P = 0.132; log-rank test). In conclusion, our observations show that accumulation of TP53 occurs frequently in the absence of mutations, and that such accumulation is nevertheless associated with poor survival when it occurs in a high proportion (> 50%) of tumour cell nuclei.