[en] A series of medical disciplines benefit from the emergence of diverse targeted therapies using monoclonal antibodies. Skin is affected by adverse events of such therapies primarily targeting internal cancers. As a unique event in medicine, some of the skin adverse effects are predictive markers of the therapeutic antineoplastic activity. This fact concerns the paroxismal acneiform eruption and the inflammatory flare-up of actinic keratoses. Such a situation is linked to the fact that these specific "unwanted" effects are not really side effects but rather represent the direct pharmacological consequence of the activity directed to the EGF receptors which are particularly abundant in the follicular ostium and in precursor lesions to skin carcinomas.