IS Ahn, et al Ann Dermatol Vol. 23, Suppl. 2, 2011 CASE REPORT http://dx.doi.org/10.5021/ad.2011.23.S2.S182 Epidermal Cysts in a Tacrolimus Treated Renal Transplant Recipient In Su Ahn, M.D., Bo Young Chung, M.D., Soo Ick Cho, M.D., Hye One Kim, M.D., Chun Wook Park, M.D., Cheol Heon Lee, M.D. Department of Dermatology, Kangnam Sacred Heart Hospital, College of Medicine, Hallym University, Seoul, Korea Tacrolimus, a calcineurin inhibitor, formerly also known as FK506, is a macrolactam drug isolated from Streptomyces tsukubaensis. Its mode of action closely parallels the action of cyclosprorin A (CsA) and can be used for the treatment of inflammatory and autoimmune skin diseases in which systemic CsA has proved effective against psoriasis, pyoderma gangrenosum, atopic dermatitis, lupus erythe- matosus and graft versus host disease (GVHD). Although several cases of epidermal cysts have been reported in patients using cyclosporine and other immunosuppressants after organ transplantation; such types of cases have yet not been reported after administration of tacrolimus. However, we report herein a case of presence of multiple, various sized epidermal cysts in a renal transplant recipient receiving tacrolimus. (Ann Dermatol 23(S2) S182∼S184, 2011) Received August 31, 2010, Revised December 7, 2010, Accepted for publication February 8, 2011 *This study was supported by a grant from Korea Healthcare Technology R&D Project, Ministry of Health and Welfare, Republic of Korea (A101550-1001-0000100). *This research was supproted by Basic Science Research Program through the National Research Foudation of Korea (NRF) funded by the Ministry of Education, Science and Technology (No.2011- 0013003). Corresponding author: Hye One Kim, M.D., Department of Derma- tology, Kangnam Sacred Heart Hospital, College of Medicine, Hallym University, 948-1 Daerim 1-dong, Youngdeungpo-gu, Seoul 150-950, Korea. Tel: 82-2-829-5221, Fax: 82-2-832-3237, E-mail: dermap@ paran.com This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http:// creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. S182 Ann Dermatol -Keywords- Epidermal cyst, FK506, Immunosuppressant, Renal trans- plant, Tacrolimus INTRODUCTION Epidermal cyst is a keratin-filled lesion lined by epidermis. It is found most commonly in both male and female adults and is presented as single or multiple, intradermal or subcutaneous masses1. This cyst is most commonly the result of plugged pilosebaceous units and can also be caused by the traumatic implantation of epidermal cells or by the proliferation of variable epidermal remnants2. Recently, human papillomavirus (HPV) type 57 and 60 DNAs have been regarded as etiological factors1,2. Immu- nomodulatory drugs, such as cyclosporine or tacrolimus are mainly used as immunosuppressants in organ trans- plantation recipients. They have recently been in the spotlight as treatment options for psoriasis, atopic der- matitis, alopecia areata and other dermatologic diseases. Tacrolimus, formerly known as FK506, is a macrolactam drug isolated from Streptomyces tsukubaensis1. Although tacrolimus has no structural homology to cyclosporine A (CsA), its mode of action closely parallels CsA, and it exerts similar in vitro effects at concentrations of 100 times lower than those of CsA3. Tacrolimus affects numerous aspects of cellular physiology, mainly alteration of gene expression in target cells. In particular, inter- leukin-(IL) 2 gene expression in CD4＋ T-helper lympho- cytes is inhibited by tacrolimus4. Although several cases of epidermal cysts have been reported in patients using cyclosporine and other immunosuppressants after organ transplantation, such types of cases have yet not been reported after administration of tacrolimus2,3,5. We report a case of presence of multiple, various sized epidermal cysts