JEADV ISSN 1468-3083 384 © 2006 The Authors JEADV 2007, 21, 384 – 387 Journal compilation © 2006 European Academy of Dermatology and Venereology Blackwell Publishing Ltd ORIGINAL ARTICLE A long-term time course of colorimetric assessment of the effects of imatinib mesylate on skin pigmentation: a study of five patients V Brazzelli,*† F Prestinari,† T Barbagallo,† C Rona,† E Orlandi,‡ F Passamonti,‡ F Locatelli,§ M Zecca,§ S Villani,¶ G Borroni† †Department of Human and Hereditary Pathology, Institute of Dermatology, ‡Institute of Hematology, §Department of Pediatrics, ¶Department of Health Sciences, Section of Medical Statistics and Epidemiology, University of Pavia, Policlinico S. Matteo IRCCS, Pavia, Italy Keywords chronic myeloid leukaemia, colorimetry, hypopigmentation, imatinib mesylate *Corresponding author, Department of Human and Hereditary Pathology, Institute of Dermatology, University of Pavia, IRCCS- Policlinico S. Matteo, Piazza C. Golgi, 2, 27100 Pavia, Italy, tel. +39 0382 503794; mobile phone +39 338 4072068; fax +39 0382 526379; E-mail: vbrazzelli@libero.it or vbrazzelli@email.it Received: 29 January 2006, accepted 2 May 2006 DOI: 10.1111/j.1468-3083.2006.01981.x Abstract Background Imatinib mesylate (IM), the first-line treatment of chronic myeloid leukaemia (CML), is a tyrosine kinase inhibitor that targets those proteins involved in BCR-ABL signal transduction in CML, c-kit (KIT) and platelet-derived growth-factor (PDGFR) receptor. The use of IM has been associated with cutaneous reactions. In the last 2 years numerous studies have focused the attention on hypopigmentations, depigmentations and photosensitivity developing after the initiation of IM therapy. Objective The aim of this study is to evaluate the effects of IM therapy on the skin pigmentation of five patients affected by CML. Methods Skin pigmentation measurements were performed with a Minolta CR-200 Chromameter. Results All the studied patients show the gradual lightening of the skin on unexposed areas over the treatment with IM. In particular, this explorative colorimetric study indicates the association between IM and skin depigment- ation with a significant increase of luminance value (L*) ( P = 0.001) and a significant decrease of the pigmentation value (b*) ( P = 0.028). Conclusion Even if we do not know the clinical significance of the skin depigmentation caused by IM, the regulatory role of KIT and its ligand stem cell factor in melanocyte development and survival seems to suggest an objective mechanism of action for IM in the pathogenesis of this cutaneous depigmentation. Introduction Imatinib mesylate (IM, Gleevec, formerly known as STI571, Novartis AG, Basel, Switzerland) represents the first-line treatment of chronic myeloid leukaemia (CML). 1–3 It acts as a potent and selective inhibitor of BCR-ABL through competitive inhibition at the adenosine triphos- phate (ATP)-binding site of the enzyme, which leads to the inhibition of tyrosine phosphorylation of proteins involved in BCR-ABL signal transduction. 4,5 It also in- hibits KIT and PDGFR receptor tyrosine kinases. 6,7 In patients with CML the use of IM was associated with cutaneous reactions with a definite dose-dependent relationship. 8–10 In the last 2 years numerous studies focused the attention on hypopigmentations, depigmentations and photosen- sitivity developing after the initiation of IM therapy. 11–18 In our previous study, we described a 17-year-old Caucasian patient affected by CML in therapy with IM, who devel- oped vitiligo-like lesions and generalized lightening of the skin. 17 The aim of this study is to evaluate through an in- strumental assessment the effects of IM therapy on skin pigmentation of five patients affected by CML.