title: The risk of second primary malignancy is increased in differentiated thyroid cancer patients with a cumulative (131)I dose over 37 GBq.
abstract: BACKGROUND
  The aim of this study was to investigate the risk factors for second primary malignancy (SPM) diagnosed after differentiated thyroid cancer (DTC).
  
  
  METHODS
  A total of 2468 DTC patients who underwent thyroidectomy were reviewed. SPM was defined as a non-thyroidal malignancy, diagnosed at least 1 year after the diagnosis of thyroid cancer. Patients were divided into five groups according to cumulative (131)I dose: very high-activity (≥ 37.0 GBq), high-activity (22.3-36.9 GBq), intermediate-activity (5.56-22.2 GBq), low-activity (1.1-5.55 GBq) and no RAI.
  
  
  RESULTS
  Among the 2468 patients, 61 (2.5%) had SPMs during 7.0 (1.0-33.0) years of median follow-up. Age above 40 years, male sex and very high-activity RAI were independent risk factors for the development of SPM. SPM-related mortality was highest in the very high-activity group, while DTC-related mortality was highest in the high-activity group. The overall mortality both from SPM and DTC was highest in the high-activity group.
  
  
  CONCLUSIONS
  A cumulative (131)I dose <37.0 GBq did not increase the risk of SPM. A cumulative (131) I dose ≥ 37.0 GBq increased the risk of SPM and SPM-related mortality and decreased the DTC-specific mortality, resulting in a similar all-cause mortality compared with the low-activity RAI group. Using repeated high-dose RAI for treating RAI-responsive but persistent DTC patients needs careful consideration of the individual benefits from RAI vs the risk of developing SPM.
authors.affiliation: Department of Internal Medicine, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: Ah Reum
authors.initials: AR
authors.lastname: Khang
authors.affiliation: Department of Internal Medicine, Seoul National University College of Medicine, Seoul, Korea.|Department of Internal Medicine, National Medical Center, Seoul, Korea.
authors.forename: Sun Wook
authors.initials: SW
authors.lastname: Cho
authors.affiliation: Department of Internal Medicine, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: Hoon Sung
authors.initials: HS
authors.lastname: Choi
authors.affiliation: Department of Internal Medicine, Seoul National University College of Medicine, Seoul, Korea.|Department of Internal Medicine, Chung-Ang University Hospital, Seoul, Korea.
authors.forename: Hwa Young
authors.initials: HY
authors.lastname: Ahn
authors.affiliation: Department of Internal Medicine, Seoul National University College of Medicine, Seoul, Korea.|Department of Internal Medicine, Dankook University Hospital, Cheonan-si, Korea.
authors.forename: Won Sang
authors.initials: WS
authors.lastname: Yoo
authors.affiliation: Department of Internal Medicine, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: Kyung Won
authors.initials: KW
authors.lastname: Kim
authors.affiliation: Department of Nuclear Medicine, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: Keon Wook
authors.initials: KW
authors.lastname: Kang
authors.affiliation: Department of Internal Medicine, Seoul National University Boramae Medical Center, Seoul, Korea.
authors.forename: Ka Hee
authors.initials: KH
authors.lastname: Yi
authors.affiliation: Department of Internal Medicine, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: Do Joon
authors.initials: DJ
authors.lastname: Park
authors.affiliation: Department of Laboratory Medicine, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: Dong Soon
authors.initials: DS
authors.lastname: Lee
authors.affiliation: Department of Nuclear Medicine, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: June-Key
authors.initials: JK
authors.lastname: Chung
authors.affiliation: Department of Internal Medicine, Seoul National University College of Medicine, Seoul, Korea.|Department of Internal Medicine, Chung-Ang University Hospital, Seoul, Korea.
authors.forename: Bo Youn
authors.initials: BY
authors.lastname: Cho
authors.affiliation: Department of Internal Medicine, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: Young Joo
authors.initials: YJ
authors.lastname: Park
mesh_terms: D018263:Adenocarcinoma, Follicular / Q000453:epidemiology / Q000532:radiotherapy*; D000328:Adult; D000367:Age Factors; D002277:Carcinoma / Q000453:epidemiology / Q000532:radiotherapy*; D002291:Carcinoma, Papillary; D015331:Cohort Studies; D005260:Female; D006801:Humans; D015994:Incidence; D007457:Iodine Radioisotopes / Q000627:therapeutic use*; D008297:Male; D008875:Middle Aged; D016609:Neoplasms, Second Primary / Q000453:epidemiology*; D011879:Radiotherapy Dosage; D018714:Radiotherapy, Adjuvant; D012189:Retrospective Studies; D012737:Sex Factors; D000077273:Thyroid Cancer, Papillary; D013964:Thyroid Neoplasms / Q000453:epidemiology / Q000532:radiotherapy*; D013965:Thyroidectomy
chemical_list: D007457:Iodine Radioisotopes