Mosaic EGFR exon 20 in-frame insertion pathogenic variants are associated with papular epidermal naevus with ‘skyline’ basal cell layer (PENS)

Papular epidermal naevus with ‘skyline’ basal cell layer (PENS) is a type of keratinocytic epidermal naevus for which the molecular genetic mechanism has not yet been identified. EGFR ex20ins could represent a new and specific genetic somatic marker of PENS.