title: Cancer risk after iodine-131 therapy for hyperthyroidism.
abstract: Cancer incidence was studied in 10,552 patients (mean age, 57 years) who received 131I therapy (mean dose, 506 MBq) for hyperthyroidism between 1950 and 1975. Follow-up on these patients was continued for an average of 15 years. Record linkage with the Swedish Cancer Register for the period 1958-1985 identified 1543 cancers occurring 1 year or more after 131I treatment, and the standardized incidence ratio (SIR) was 1.06 (95% confidence interval = 1.01-1.11). Significantly increased SIRs were observed for cancers of the lung (SIR = 1.32; n = 105) and kidney (SIR = 1.39; n = 66). Among 10-year survivors, significantly elevated risks were seen for cancers of the stomach (SIR = 1.33; n = 58), kidney (SIR = 1.51; n = 37), and brain (SIR = 1.63; n = 30). Only the risk for stomach cancer, however, increased over time (P less than .05) and with increasing activity administered (P = not significant). The risk for malignant lymphoma was significantly below expectation (SIR = 0.53; n = 11). Overall cancer risk did not increase with administered 131I dose or with time since exposure. The absence of any increase in leukemia adds further support to the view that a radiation dose delivered gradually over time is less carcinogenic than the same total dose received over a short time. Only for stomach cancer was a possible radiogenic excess suggested.
authors.affiliation: Department of Cancer Prevention, Radiumhemmet, Karolinska Hospital, Stockholm, Sweden.
authors.forename: L E
authors.initials: LE
authors.lastname: Holm
authors.forename: P
authors.initials: P
authors.lastname: Hall
authors.forename: K
authors.initials: K
authors.lastname: Wiklund
authors.forename: G
authors.initials: G
authors.lastname: Lundell
authors.forename: G
authors.initials: G
authors.lastname: Berg
authors.forename: G
authors.initials: G
authors.lastname: Bjelkengren
authors.forename: E
authors.initials: E
authors.lastname: Cederquist
authors.forename: U B
authors.initials: UB
authors.lastname: Ericsson
authors.forename: A
authors.initials: A
authors.lastname: Hallquist
authors.forename: L G
authors.initials: LG
authors.lastname: Larsson
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D015331:Cohort Studies; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D006980:Hyperthyroidism / Q000532:radiotherapy*; D007457:Iodine Radioisotopes / Q000009:adverse effects* / Q000627:therapeutic use; D007938:Leukemia / Q000453:epidemiology / Q000209:etiology; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000453:epidemiology / Q000209:etiology*; D012307:Risk Factors; D013548:Sweden / Q000453:epidemiology
chemical_list: D007457:Iodine Radioisotopes