Thyroid Abnormalities

Hypothyroidism. Risk factors for hypothyroidism include increasing dose of radiation, female sex, and older age at diagnosis.[21-23] CCSS investigators reported a 20-year actuarial risk of 30% of developing hypothyroidism in Hodgkin lymphoma survivors treated with 35 Gy to 44.99 Gy of radiation and 50% for subjects whose thyroid received 45 Gy or more of radiation.Hypothyroidism develops most often in the first 5 years after treatment, but new cases have emerged more than 20 years after the cancer diagnosis.[22]

Hyperthyroidism. Hyperthyroidism has been observed after treatment for Hodgkin lymphoma, with a clinical picture similar to that of Graves' disease.[24] Higher radiation dose has been associated with greater risk of hyperthyroidism.[22]

Subsequent neoplasms. Thyroid neoplasms, both benign and malignant, have been reported with increased frequency after neck irradiation. The incidence of nodules varies substantially across studies (2%–65%) depending on the length of follow-up and detection methods used.[21-23] The relative risk (RR) of thyroid cancer is higher among Hodgkin lymphoma survivors (approximately 18-fold for the CCSS Hodgkin lymphoma cohort compared with the general population).[23] Risk factors for the development of thyroid nodules in Hodgkin lymphoma survivors reported by CCSS include time since diagnosis of more than 10 years (RR, 4.8; 95% confidence interval [CI], 3.0–7.8), female sex (RR, 4.0; 95% CI, 2.5–6.7), and radiation dose to thyroid higher than 25 Gy (RR, 2.9; 95% CI, 1.4–6.9).[23] The absolute risk of thyroid cancer is relatively low, with approximately 1% of the CCSS Hodgkin cohort developing thyroid cancer, with a median follow-up of approximately 15 years.[23] A single-institution Hodgkin lymphoma survivor cohort that included both adult and pediatric cases showed a cumulative incidence of thyroid cancer at 10 years from diagnosis of 0.26%, increasing to approximately 3% at 30 years from diagnosis. In this cohort, age younger than 20 years at Hodgkin lymphoma diagnosis and female sex were significantly associated with thyroid cancer.[25]