Research Article For reprint orders, please contact: reprints@futuremedicine.com Changing pattern of secondary cancers among patients with malignant thymoma in the USA Vivek Kumar* ,1 , Mohit Garg 2 , Abhishek Goyal 1 , Neha Chaudhary 3 , Parita Soni 4 & Abhinav Binod Chandra 5 1 Department of General Internal Medicine, Brigham & Women’s Hospital, Boston, MA 02115, USA 2 Department of Anesthesia, Maimonides Medical Center, New York, NY 11219, USA 3 Department of Pediatrics, Beth Israel Deaconess Medical Center, Boston, MA 02115, USA 4 Department of Pulmonary and Critical Care Medicine, Maimonides Medical Center, New York, NY 11219, USA 5 Department of Medical Oncology, Yuma Regional Medical Center, Cancer Center Yuma, AZ 85364, USA *Author for correspondence: Tel.: + 1347-525-8607; abhinavbck@hotmail.com Background: The risk of developing secondary cancers (SCs) among patients with malignant thymoma in the US has not been estimated in the more recent time period. Methods: We extracted demographic and treatment data from the SEER database to estimate the standardized incidence ratios (SIRs). Results: Of 1570 patients with thymoma 211 (13.4%) had SCs. The overall risk of developing SCs was higher among patients with thymoma (SIR: 1.54, 95% CI: 1.34–1.76). The SIRs for cancers of lung, esophagus, sigmoid colon, soft tissue and heart, kidney, NHL and leukemia was signifcantly higher as compared to the general US population. Conclusions: Patients with thymoma are at modestly elevated risk of developing SCs as compared to the general US population. Although the overall risk has not changed after 14 additional years of follow up, the distribution of SCs has signifcantly broadened, with increased diversity across type and anatomic location of SCs First draft submitted: 13 November 2017; Accepted for publication: 9 February 2018; Published online: 7 August 2018 Keywords: AER • epidemiology • hematological malignancies • latency period • population-based registry • sec- ondary cancer • SEER • SIR • solid tumors • thymoma Thymoma is a rare malignancy in the USA with an estimated incidence of approximately one case per 1 million of the population [1]. In the USA, it is more prevalent among Asians and Pacific Islanders for unknown reasons [2]. Its incidence increases with age, peaking in the seventh decade [2]. The increased risk of secondary cancers (SCs) in patients with thymoma has been previously reported in the literature through data from single centers as well as from population-based registries [3–6]. The higher risk of SCs among these patients has been attributed to immune dysregulation, genetic and environmental factors [7,8]. Friedman et al. reported higher risk of hematological malignancies among these patients [9]. In another study from John Hopkins, Welsh et al. reported 31% prevalence of additional neoplasms in patients with thymoma [10]. Travis et al. analyzed patients with thymoma in the SEER database diagnosed up until 2000 and reported a modest increase in the risk of SCs among these patients [5]. Overall these patients were at 1.5-times higher risk of developing SCs as compared with the general US population. The higher risk as compared with the general US population was observed for the digestive tract cancers, non-Hodgkin’s lymphoma (NHL) and sarcoma. Another study using the SEER database up until 2007, compared the risk of all pre- and postdiagnosis extrathymic cancers among patients with thymoma and reported seven- and 18-times higher risk, respectively [6]. However, there is no data on the risk of SCs among these patients from this point forward. In this longitudinal analysis, we aim to estimate the risk of SCs among patients with thymoma during this prolonged period of follow-up. We also stratified the risk of developing SCs according to the age of thymoma diagnosis, gender, type of treatment and follow-up period in this patient population. Future Oncol. (Epub ahead of print) ISSN 1479-6694 10.2217/fon-2017-0626 C  2018 Future Medicine Ltd