PTEN and anus adenocarcinoma: 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.