Keratinocytic epidermal nevus with ipsilateral breast hypoplasia

Breast hypoplasia has been reported in some epidermal nevus syndromes, but not with a keratinocytic epidermal nevus. Herein, we describe the first case of breast hypoplasia associated with a keratinocytic epidermal nevus. Keratinocytic epidermal nevi have been shown to be associated with somatic mutations in FGFR3, PIK3CA, and HRAS. We hypothesize that hypoplasia may be due to a local mutation in the FGFR3 gene or increased androgen receptors in affected breast tissue. The patient was treated with CO₂ laser with good cosmetic outcome.