1164 Neoplasma 2020; 67(5): 1164–1169 doi:10.4149/neo_2020_200214N131 Total body irradiation is a crucial risk factor for developing secondary carcinomas afer allogeneic hematopoietic stem cell transplantation in childhood P. KESLOVA 1, *, R. FORMANKOVA 1 , P. RIHA 1 , L. SRAMKOVA 1 , M. SNAJDEROVA 2 , B. MALINOVA 3 , A. LUKS 1 , J. STERBA 4 , J. STARY 1 , P. SEDLACEK 1 1 Department of Pediatric Hematology and Oncology, University Hospital Motol, 2 nd Medical School, Charles University Prague, Prague, Czech Republic; 2 Department of Pediatrics, University Hospital Motol, 2 nd Medical School, Charles University Prague, Prague, Czech Republic; 3 Department of Oncology, University Hospital Motol, 2 nd Medical School, Charles University Prague, Prague, Czech Republic; 4 Department of Pediatric Oncology, University Hospital Brno and School of Medicine, Masaryk University, Brno, Czech Republic *Correspondence: petra.keslova@fnmotol.cz Received February 14, 2020 / Accepted March 30, 2020 Allogeneic hematopoietic stem cell transplantation (HSCT) has become a standard part of therapy for a variety of malignant and non-malignant disorders. With improved outcomes afer HSCT, increasing attention has been drawn to late complications in long-term survivors. Te development of secondary malignancies is recognized as one of the most serious complications. We have evaluated data from 426 patients (272 males, 154 females) who underwent allogeneic transplanta- tion at a median age of 7.9 years from 1989 till 2017 and were alive more than one year afer transplantation for the occur- rence of secondary solid tumors. We have documented the occurrence of secondary solid tumors in 20 patients (4.7%). Te median duration of the development of secondary solid cancer from HSCT was 11.7 (range, 5.4–21.5 years). 18 out of 20 patients (90%) had total body irradiation (TBI) 12–14.4 Gy as a part of a conditioning regimen. All but two had transplanta- tion for malignant disease. All patients underwent surgery and/or chemo-radiotherapy. Eighteen are alive, and two died due to the progression of their secondary malignancy. Te most frequent solid cancer was thyroid carcinoma (n=9). Cumula- tive incidence of secondary solid cancer in all groups was 15.2±3.9%, in a group using TBI based regimen 34.7±8.9%, in non-TBI (only chemo) group was 1.5±1.1%. Overall, the cumulative incidence is statistically signifcantly diferent between the TBI based and non-TBI (chemo only) group. Te incidence and number of complications following allogeneic HSCT in childhood are increasing in time. Te early diagnosis of secondary malignancies is one of the key tasks of long-life multi- disciplinary post-transplant care. Key words: total body irradiation, secondary carcinoma, allogeneic hematopoietic stem cell transplantation, childhood, risk factor, chronic graf versus host disease Allogeneic hematopoietic stem cell transplantation (HSCT) has become a standard part of therapy for a variety of malignant and non-malignant disorders. Te number of HSCT survivors is growing [1], with a current estimate of one half million worldwide. Long term survivors are at high risk for many late efects including the development of subse- quent solid cancer [2]. Te incidence of second cancers is two-eight-fold higher than the rate expected in the general adult population and being in 2–6% at ten years and 6–13% at ffeen years afer HSCT. Te increased rate of second cancers may be a result of chemotherapy and radiation conditioning used for transplantation, immunosuppression, immune dysregulation afer transplantation, the chemotherapy, and radiotherapy the patient received before transplantation [3]. Much of the long-term complication, including the develop- ment of second cancers has been carried out in a combina- tion of adults and children or adult patient population only, and survival and outcome observed in these cohorts may not refect the expected results among pediatric transplanted patients. Children may be mainly at increased risk secondary to their long-life expectancy and potentially increased sensitivity of proliferating tissue to carcinogens. Tose who undergo allogeneic HSCT are at signifcantly increased risk of secondary cancers compared with pediatric cancer survivors treated without HSCT [4, 5]. Te risk of radiation-induced second cancers is well described in the pediatric Hodgkin disease population. Bhatia et al. [6] reported the cumulative incidence for second solid malignancy at 7.3% at 20 years, increasing to 23.5% at 30 years. Breast cancer was a common solid malignancy, followed by thyroid, bone, colorectal, and