Patients with hyperthyroidism who were treated with radioiodine (RAI) or thyroidectomy did not experience an increased overall risk for cancer, but they did face a higher risk for gastric and respiratory cancers, new data published in the Journal of Clinical Endocrinology & Metabolism indicate.
Previous studies have demonstrated a relationship between cancer incidence and cancer mortality in patients with hyperthyroidism treated with RAI, with some suggesting that RAI dose may be a factor. However, the data are conflicting, the researchers noted. Further, most research has not assessed how other treatments, such as thyroidectomy, may influence cancer risk.
To assess cancer risk in this patient population, the researchers evaluated 4,334 patients who underwent thyroidectomy and 1,814 who underwent RAI for treatment of hyperthyroidism from 1986 to 2007 in Finland. They also included three age- and gender-matched controls per each treated patient in their analysis.
Follow-up started 3 months after treatment and lasted until cancer diagnosis, death, emigration or Dec. 31, 2009.
Although patients with hyperthyroidism did not have an increased overall cancer incidence when compared with control patients (RR=1.05; 95% CI, 0.96-1.15), they did have an increased risk for respiratory tract cancers (RR=1.46; 95% CI, 1.05-2.02) and stomach cancers (RR=1.64; 95% CI, 1.01-2.68).
Results did not delineate a difference in cancer mortality between the control patients and those with hyperthyroidism (RR=1.08; 95% CI, 0.94-1.25). Additionally, treatment type did not affect overall risk for cancer (HR for RAI vs. thyroidectomy, 1.03; 95% CI, 0.86-1.23) or risk for cancer mortality (HR=1.04; 95% CI, 0.91-1.21).
“Based on this large-scale, long-term follow-up study, the increased cancer risk in hyperthyroid patients is attributable to hyperthyroidism and shared risk factors, not the treatment modality,” the researchers concluded.