Preneoplastic and neoplastic diseases successfully treated with retinoids include oral leukoplakia, cervical dysplasia and xeroderma pigmentosum (premalignant), and acute promyelocytic leukemia (APL), a malignant condition characterized by altered signalling through both the promyelocyte leukemia protein (PML) and retinoic acid receptor α (RARα) [25], [38]. Here, PML is linked to xeroderma pigmentosum.