The cutaneous abnormalities of a fully developed example of xeroderma pigmentosum appear to have been at least temporarily ameliorated by the oral administration of methoxsalen over a period of five years.
NOOJIN RO. Xeroderma Pigmentosum Treated With Oral MethoxsalenA Case Report. Arch Dermatol. 1965;92(4):422–423. doi:10.1001/archderm.1965.01600160078017