However, somatic mutations in one or several downstream effector(s) of the EGFR signalling pathway were clearly shown to be associated to resistance to anti-EGFR drugs (cetuximab and panitumumab).28,29 Therefore, the prevalence rates of KRAS, NRAS, BRAF, PIK3CA, EGFR, HER2 and PTEN mutations were determined in all collected anal adenocarcinoma specimens. Here, PIK3CA is linked to anus adenocarcinoma.