Correlation of p53 immunoreactivity and sequencing in patients with glioma

This study examines the relationship between p53 immunostaining and direct sequencing of polymerase chain reaction (PCR) products in 61 gliomas. Glioma tissues obtained from patients at surgery were analyzed immunohistochemically with the monoclonal antibody PAb1801 to detect p53 protein abnormalities. Amplified p53 cDNA from these samples was analyzed by direct sequencing. Four grades of p53 immunostaining were evaluated: grade 0 = no labeling, grade 1 = less than 5% labeled cells, grade 2 = 5-30% labeled cells, and grade 3 = more than 30% labeled cells. Twenty-six of 36 glioblastomas, 14 of 23 anaplastic gliomas, and none of two low-grade gliomas had positive p53 immunoreactivity. Direct sequencing of PCR-amplified p53 cDNA revealed that 10 glioblastomas, 11 anaplastic gliomas, and no low-grade gliomas had mutations. Comparison of p53 immunostaining and sequencing data revealed that among all the gliomas, mutations were found in three of 21 with p53 grade 0, one of 16 with p53 grade 1, seven of nine with p53 grade 2, and 10 of 15 with p53 grade 3. These results indicate a good correlation between the p53 immunostaining and sequencing data when the percentage of abnormal cells within the tumor was greater than 5% (p53 grades 2 and 3). However, the correlation was poor when the percentage of abnormal cells was less than 5% (p53 grade 1) because of the limited sensitivity of sequencing techniques. Thus, p53 immunostaining may be more accurate in detecting p53 alterations when the percentage of abnormal cells is small; however, in rare cases, p53 immunostaining may fail to detect mutations confirmed by sequencing.