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Thyroid radiation dose, other factors may predict carcinoma risk after childhood cancer
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Several factors besides thyroid radiation dose may predict thyroid carcinoma risk in childhood cancer survivors, including the type of chemotherapy, radiation dose to the pituitary gland and obesity, according to research in The Journal of Clinical Endocrinology & Metabolism.
Florent de Vathaire, PhD, of the French Institute of Health and Medical Research, and colleagues analyzed data from 4,338 5-year survivors of solid-tumor cancers treated before 1986 and age 16 years. All patients were treated in France (n = 3,127) or the United Kingdom (n = 1,211). Researchers followed the cohort for an average of 27 years, reconstructing actual conditions for patients to determine radiotherapy doses to the thyroid gland and other sites.
Within the cohort, 55 patients developed a thyroid carcinoma requiring surgery (51 papillary; four follicular), with the risk for thyroid carcinoma increasing with a radiation dose of up to 0.2 Gy, but leveling off for higher doses, according to researchers.
“The incidence of thyroid cancer was 20 times higher than expected from the general population, with a cumulative incidence of 2.4%, 40 years after childhood cancer treatment,” the researchers wrote. “This very high increase as compared to the general population was observed mainly 10 to 20 years after childhood cancer treatment and decreased thereafter. However, the [absolute excess risk] remained stable during follow-up.”
Chemotherapy as a whole did not increase the risk for thyroid cancer and did not modify the thyroid radiation dose-response; however, patients who received nitrosoureas had an increased RR of 6.6 (95% CI, 2.5-15.7). Patients who had a surgical or radiologic splenectomy had an increased RR of 2.3 (95% CI, 1.3-4), whereas patients who received radiation doses greater than 5 Gy to the pituitary gland had a reduced risk for thyroid cancer (RR = 0.2; 95% CI, 0.1-0.6).
Researchers found no significant relationship between BMI and thyroid cancer when analyzing BMI as a continuous variable. However, patients with a BMI of 25 kg/m² or greater had an increased risk per gray of radiation to the thyroid (RR = 7.6; 95% CI, 1.6-33.3) when compared with those who had a lower BMI (RR = 4.1; 95% CI, 0.9-17.7). Researchers found no association between thyroid cancer risk and the smoking status of patients. – by Regina Schaffer
Disclosure: The researchers report no relevant financial disclosures.
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