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Study links RAI dose, second primary malignancy in thyroid cancer
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Treatment with radioactive iodine increased the risk for second primary malignancy among patients with thyroid cancer, according to the results of a population-based study.
The risk appeared particularly elevated among patients who received cumulative radioactive iodine (RAI) doses greater than 150 mCi, results showed.
RAI is widely used for thyroid cancer treatment. However, few studies have investigated the association between RAI exposure and second primary malignancy.
Chia-Jen Liu, MD, of the division of hematology and oncology at Taipei Veterans General Hospital in Taiwan, and colleagues conducted a nationwide population-based study of patients with newly diagnosed thyroid cancer in Taiwan between 1997 and 2010.
They used the Taiwan National Health Insurance database to identify 20,235 patients (median age, 46 years; interquartile range, 36-56), with a combined follow-up of 134,178 person-years.
The researchers identified 692 cases of second primary malignancy from this cohort. They calculated a standardized incidence ratio (SIR) for any second primary malignancy of 1.41 (95% CI, 1.31-1.52).
Significantly high SIRs occurred for leukemia (SIR = 2.74; 95% CI, 1.65-4.28), non-Hodgkin’s lymphoma (SIR = 2.38; 95% CI, 1.55-3.48), prostate cancer (SIR = 2.3; 95% CI, 1.49-3.4), lung and mediastinum cancers (SIR = 1.93; 95% CI, 1.58-2.35), pancreatic cancer (SIR = 1.83; 1.02-3.02), kidney cancer (SIR = 1.81; 95% CI, 1.15-2.72), breast cancer (SIR = 1.48; 95% CI, 1.25-1.72), and colorectal cancer (SIR = 1.31; 95% CI, 1.06-1.61).
Cumulative RAI dose predicted risk for second primary malignancy (adjusted HR per 30 mCi increase = 1.01; 95% CI, 1.01-1.02), as well as leukemia (adjusted HR = 1.03; 95% CI, 1.02-1.04).
Further, a cumulative RAI dose greater than 150 mCi resulted in a statistically significant risk for all cancers (adjusted HR = 1.3) and leukemia (adjusted HR = 6.03).
The researchers acknowledged limitations of their study, including a lack of information about confounding factors such as occupational or environmental radiation exposure, tobacco or alcohol use, obesity and family history of malignancy. Further, pathological type and stage of each thyroid cancer were not available in the dataset.
“Overall, it is recommended that fewer patients receive high doses of RAI for the treatment of thyroid cancer; a low fixed dose or dosimetric method would be more favorable strategies,” Liu and colleagues wrote. “For those whose disease burden necessitates a higher RAI dose, we suggest a more thorough survey to investigate clinically suspicious symptoms of second primary malignancy.” – by Cameron Kelsall
Disclosure: The researchers report no relevant financial disclosures.
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