Mutational analysis of tumor suppressor gene p53 in feline vaccine site-associated sarcomas

Objectives-To investigate the role of tumor suppressor gene p53 mutation in feline vaccine site-associated sarcoma (VSS) development and to evaluate t he relationship between p53 nucleotide sequence and protein expression. Sample Population-Formalin-fixed paraffin-embedded tissues of 8 feline VSS with dark p53 immunostaining thigh p53 expression) and 13 feline VSS with f aint or no staining (normal p53 expression). Procedure-DNA was extracted from neoplastic and normal tissue from each par affin block. The following 3 regions of the p53 gene were amplified by poly merase chain reaction: 379 base pair (bp) region of exon 5, intron 5, and e xon 6, 108 bp region of exon 7 and 140 bp region of exon 8. Amplified p53 p roducts were sequenced and compared with published feline p53. The p53 muta tions identified were correlated with p53 mutations predicted by immunostai ning. Results-Neoplastic cells of 5 of 8 (62.5%) VSS that had high p53 expression harbored single missense mutations within the p53 gene regions examined. T he p53 gene mutations were not detected in the 13 tumors with normal p53 im munostaining. Nonneoplastic tissues adjacent to all 21 VSS lacked mutations of these p53 gene regions. Conclusions-The p53 gene mutations were restricted to neoplastic tissue and , therefore, were unlikely to predispose to VSS. However, p53 mutations may have contributed to cancer progression in 5 of the 21 VSS. There was very good (kappa quotient = 0.67 with a confidence limit of 0.3 to 1.0), althoug h not complete, agreement between prediction of mutation by p53 immunostain ing and identification of mutations by sequencing of key p53 gene regions.