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Cancer mortality after iodine-131 therapy for hyperthyroidism
P Hall1, G Berg, G Bjelkengren
1Department of General Oncology, Radiumhemmet, Karolinska Hospital, Stockholm, Sweden.
International Journal of Cancer
|April 11, 1992
Summary
This study found a slight increase in cancer mortality among Swedish hyperthyroid patients treated with radioactive iodine (131I). While overall cancer risk was elevated, specific cancers like leukemia and breast cancer showed no increased risk.
Area of Science:
- Endocrinology
- Oncology
- Nuclear Medicine
Background:
- Hyperthyroidism is a common endocrine disorder.
- Radioactive iodine (131I) therapy is a standard treatment for hyperthyroidism.
- Long-term cancer risks associated with 131I therapy require ongoing investigation.
Purpose of the Study:
- To investigate cancer mortality in a large cohort of Swedish patients treated with 131I for hyperthyroidism.
- To assess the relationship between 131I dose, time since exposure, and cancer risk.
- To identify specific cancer types potentially linked to 131I treatment.
Main Methods:
- A cohort of 10,552 Swedish hyperthyroid patients treated with 131I (1950-1975) was established.
- Patients were linked to the Swedish Cause-of-Death Register to track cancer and leukemia mortality.
- Standardized mortality ratios (SMRs) were calculated and analyzed based on time since exposure, patient demographics, and treatment characteristics.
Main Results:
- Overall cancer mortality showed a modest increase (SMR = 1.09), particularly in women.
- Elevated risk for digestive tract and respiratory cancers was observed more than 10 years post-exposure.
- No increased risk for leukemia, bladder, or breast cancer was found. Younger patients and higher 131I activity correlated with higher SMRs.
Conclusions:
- The study suggests 131I therapy may contribute to excess mortality from specific cancers, notably stomach cancer.
- The observed patterns do not strongly support a general carcinogenic effect of 131I over the long term.
- Further research is warranted to elucidate the complex relationship between 131I and cancer risk.