Cancer risk after iodine-131 therapy for hyperthyroidism.
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.
Holm
L E
LE
Department of Cancer Prevention, Radiumhemmet, Karolinska Hospital, Stockholm, Sweden.
Hall
P
P
Wiklund
K
K
Lundell
G
G
Berg
G
G
Bjelkengren
G
G
Cederquist
E
E
Ericsson
U B
UB
Hallquist
A
A
Larsson
L G
LG
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
D007457:Iodine Radioisotopes