557 A case of acquired dermal melanocytosis associated with Imatinib mesylate treatment

Abstract

Imatinib mesylate is a tyrosine kinase inhibitor (TKI) that regulates cell growth, thereby inhibiting cancer cell proliferation. It has been used to treat various neoplasms such as chronic myeloid leukemia (CML). The most common side effect in skin is hypopigmentation. However, hyperpigmentation has also been rarely reported. A 48-year-old woman diagnosed as chronic myeloid leukemia presented with bluish to grayish macules and patches on face, shoulder, and buttock. She had got a treatment of CML with imatinib mesylate for 9 years. She complained hyperpigmentation on face 3 years after the imatinib mesylate treatment. Additionally, the patient reported diffuse bluish to brownish hyperpigmentation similar to Mongolian spot on the upper trunk and buttock appearing about 2 years ago. Histopathologic examination revealed brownish pigmentation of melanin in dermis with dendritic and stellate-shaped dermal melanocytes. In immunohistochemistry, the cells were positive for S-100, Melan-A, and HMB-45. Based on these pathologic findings considering with temporal relationship between the treatment and the clinical manifestations, the diagnosis of an imatinib-induced acquired dermal melanocytosis was made. Imatinib mesylate induces KIT and its ligand stem cell factor (SCF) which inhibits the production of melanin from melanocytes, leading to hypopigmentation. However, some theories postulated it could have different target effects on melanocytes, suggesting melanin production of immature melanocytes could be promoted by imatinib mesylate. In our case, the patient showed hyperpigmentation on typical locations of congenital nevi such as Mongolian spots and nevus of Ito rather than usual locations of the acquired dermal melanocytosis including forehead and zygomatic region. Herein, we report a case of acquired dermal melanocytosis induced by imatinib mesylate, which suggests that immature melanocytes are predominantly distributed in specific areas.