The cohort was divided into two distinct phenotypes; patients with grade 3 (or higher) toxicity and patients with no or up to grade 2 skin toxicity It was chosen to do so since the occurrence of grade 3 toxicity is of significant clinical relevance; toxicity of this severance might interfere with anti-tumor efficacy due to the need for dose reductions, dose delays and, in some cases, even permanent discontinuation of the EGFR inhibitor. This evidence concerns the gene EGFR and dermatological toxicity.