BRCA1 and neoplasm: However, TP53 mutations were only found in those BRCA1 methylated tumours that exhibited absent or markedly reduced BRCA1 expression, in which case the TP53 mutation frequency becomes 55.5% (5 of 9) and the association statistically significant (P = 0.01317, OR = 6.13, 95%CI = 1.21–33.51; Table 2).