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Background  Breast cancer (BC) is known to be the most common malignancy in females whereas colorectal cancer (CRC) incidence also higher in both genders in Sri Lanka.  TP53  is an important tumour suppressor gene and its somatic mutations are reported in approximately 27% of BC and 43% of CRC cases. Analysis of  TP53  gene variants not only provides clues for the aetiology of the tumour formation, but also has an impact on treatment efficacy. The current study was conducted to investigate the pattern of  TP53  variants in patients with BC and CRC from Sri Lanka.    Methods  30 patients with BC, 21 patients with CRC and an equal number of healthy controls were screened for mutational status of  TP53  by polymerase chain reaction (PCR) followed by direct sequencing. In addition, a subset of these samples were analysed for the protein expression of p53 and comparison made with the mutational status of  TP53 . We also analysed the protein expression of p21 and MDM2 as potential indicators of p53 functional status and compared it with the protein expression of p53. Additionally, hotspot codons of the  KRAS, BRAF  and  PIK3CA  genes were also analysed in a subset of CRC patients.    Results  Twenty seven sequence variants, including several novel variants in the  TP53  gene were found. Nine BC and seven CRC tumour samples carried pathogenic  TP53  variants. Pathogenic point missense variants were associated with strong and diffuse positive staining for p53 by immunohistochemistry (IHC), whereas, wild type  TP53  showed complete absence of positive IHC staining or rare positive cells, regardless of the type of cancer. There was no direct correlation between p21 or MDM2 expression and p53 expression in either BCs or CRCs. Four of the CRC patients had pathogenic hotspot variants in  KRAS ; three of them were on codon 12 and one was on codon 61.    Conclusion  The prevalence of pathogenic somatic  TP53  variants was 31 and 33.33% in the studied BC and CRC cohorts respectively. All of them were located in exons 5–8 and the pathogenic missense variants were associated with strong immuno-positive staining for p53.

bmc cancer

Pattern of nucleotide variants of TP53 and their correlation with the expression of p53 and its downstream proteins in a Sri Lankan cohort of breast and colorectal cancer patients