Staining patterns of p53 immunohistochemistry and their biological significance in colorectal cancer

Immunohistochemistry (IHC) is a cheap and rapid method to detect p53 inacti vation but the results are often discordant with gene mutation analysis, Th is study aimed to investigate whether there is a difference in the immunohi stochemical staining patterns of p53-positive cells on comparing tumours wi th inactivating gene mutations with those without. Tissues of 142 colorecta l cancers were investigated for p53 inactivation simultaneously by IHC and gene analysis using SSCP of exons 4-9 and sequencing. In addition, tumours were investigated immunohistochemically for the expression of mdm-2 protein , known to be transcriptionally transactivated by the wild-type (wt) p53 ge ne. p53-positive cells of tumours without detectable p53 gene mutations wer e microdissected using a PALM laser microscope system and subjected to p53 sequence analysis, Among the 142 cases of colorectal cancer (male/female = 88/54; mean age 66a +/- 11 years, range 24-90 Sears), 74% (n = 105) of tumo urs were positive by p53 IHC and mutations in the p53 gene were found in 51 % (73 patients). In 16% (12 patients) with mutations in the p53 gene, IHC f or p53 was negative, In tumours with mutations in the p53 gene and positive p53 IHC, staining of all nuclei of the tumour was more frequently (57/61, 93%) found than in tumours without p53 gene mutations, where staining of sc attered single cells was predominantly seen (29/44, 66%; p < 0.0001). mdm-2 positivity (n = 33) showed only staining of scattered single cells, predom inantly (24/33, 82%; p < 0.0001) in tumours without gene mutations, Single cell microdissection followed by mutation analysis of scattered p53-positiv e cells revealed no gene mutations. A scattered positive immunohistochemica l reactivity of p53 in colorectal cancer cells might therefore represent a functionally active non-mutated p53 gene and should not be considered as a marker of gene mutation and inactivation. Copyright (C) 2000 John Wiley & S ons, Ltd.