Received: 19 March 2020 Revised: 26 April 2020 Accepted: 2 May 2020 DOI: 10.1002/pbc.28422 Pediatric Blood & Cancer The American Society of Pediatric Hematology/Oncology BRIEF REPORT The annual incidence of Langerhans cell histiocytosis among adults living in Greece Polyzois Makras 1 Dimitra Stathi 2 Maria Yavropoulou 1,3 Marina Tsoli 1,3 Gregory Kaltsas 1,3 1 Department of Medical Research, LCH Adult Clinic, 251 Hellenic Air Force General Hospital, Athens, Greece 2 2nd Department of Internal Medicine, 251 Hellenic Air Force General Hospital, Athens, Greece 3 Endocrinology Unit, 1st Department of Propedeutic Internal Medicine, National and Kapodistrian University of Athens Medical School, LAIKO General Hospital of Athens, Athens, Greece Correspondence Polyzois Makras, Department of Medical Research, LCH Adult Clinic, 251 Hellenic Air Force General Hospital, 3 KanellopoulouStr, 115 25 Goudi, Athens, Greece. Email: pmakras@gmail.com Polyzois Makras and Dimitra Stathi share first authorship. Abstract Langerhans cell histiocytosis (LCH) is a rare inflammatory myeloid neoplasia with a variable clinical course and outcome. Although there are some data regarding its incidence in children, such infor- mation in adults is lacking. To address the actual annual LCH incidence among adults, we prospec- tively recorded, during a 12-month period, any new case with a definitive histological diagnosis of LCH, among persons aged 18 and older living in Greece. Fourteen new cases were recorded corre- sponding to an annual incidence of 1.58 per million population. Female to male ratio was 1.34, and mean age at diagnosis was 43.5 years. KEYWORDS adults, incidence, Langerhans cell histiocytosis 1 INTRODUCTION Langerhans cell histiocytosis (LCH) is a rare inflammatory myeloid neoplasia of unknown etiology with a variable clinical course and outcome. 1,2 Worldwide, LCH is more often encountered in children, with a median age at diagnosis of 3 years old, with an estimated annual incidence of up to 8.9 cases per million in children younger than 15 years and a male to female ratio of 2:1. 3,4 Globally, in adults it is probably rarer than children and is regarded as an “orphan dis- ease”, with an estimated incidence from pediatric series of one to two cases per million per year, and a mean age at diagnosis of 33 years, 5 although an equivalent with children’s incidence has also been proposed. 6 To address the clinically important issue of the actual annual LCH incidence among adults in Greece, we prospectively recorded all new cases with a definitive diagnosis of LCH in all regional histopatholog- ical units in Greece among individuals older than 18 years during a 12-month period. Abbreviations: BAL, bronchoalveolar lavage; LCH, Langerhans cell histiocytosis. 2 METHODS From September 1, 2018 until August 31, 2019, all new cases with a definitive LCH diagnosis 1 were prospectively recorded at a national level using two methods. The first was through the pathology lab- oratories operating in the Greek health care system. Specifically, a total of 102 out of 120 public and private pathology laboratories in Greece were included, reaching an overall response rate of 85%; fol- lowing initial information about the primary aims of the study, regular (every 3 months) communication was established in order to record all new histologically confirmed cases. All 102 pathology laboratories that were finally included in this study responded at all five points of com- munication (baseline, 3 months, 6 months, 9 months, and 12 months). Cases with a suggested LCH diagnosis based solely on the percentage of CD1a positive (+) cells of the bronchoalveolar lavage (BAL) were not included. In accordance with the General Data Protection Regulation (GDPR) and in order to avoid duplicate reporting, patients’ initials, age, sex, ethnicity, type of tissue, previous history of LCH, and, when possi- ble, the number of systems affected were recorded in each case. To avoid missing cases diagnosed abroad, we also used a sec- ond method of ascertainment through the Artemis Association for Pediatr Blood Cancer. 2020;e28422. c ○ 2020 Wiley Periodicals, Inc. 1 of 3 wileyonlinelibrary.com/journal/pbc https://doi.org/10.1002/pbc.28422