Postzygotic KRAS G12C Mutation Associated with Various Malignancies Also Underlying Epidermal Nevus Syndrome

The document reports a case of a three-year-old Japanese girl with epidermal nevus syndrome (ENS), a condition characterized by the presence of epidermal nevi and systemic involvement. This is the first reported case of ENS caused by a postzygotic KRAS G12C mutation, a mutation previously associated with various carcinomas and sarcomas but not with ENS. The patient exhibited two types of nevi, yellowish plaques suggesting sebaceous nevus on the head and face, and dark brownish verrucous plaques suggesting keratinocytic epidermal nevus on the trunk and lower extremity. Mutation analysis revealed the KRAS c.34G>T p.G12C mutation in the DNA from her lesional epidermis but not in nonlesional epidermis or peripheral blood leukocytes. Although no malignant tumors had developed by the age of three, regular follow-up was recommended due to the association of the mutation with malignancies.