Metso et al.1, 2 recently reported increased cancer mortality in hyperthyroid patients treated by radioiodine. Major limitations of those works, as lacking of hyperthyroid controls, were correctly discussed by the authors. However, in our opinion the evaluation of administered activity and associated mortality risk should be biased. In fact, the analysis was performed on 3 subgroups (ie, patients treated by 55–258 MBq, 259–369 MBq, and 370–2664 MBq, respectively) and increased mortality was observed only in the latter. Because 1) mean administered activity was 305 MBq, 2) only 24% of patients received more than 370 MBq, and 3) the 370–2664 MBq is a very wide range, more detailed analysis of the activity received by patients who died after radioiodine is needed. In fact, activities more than 600–740 MBq are not usually administered to treat hyperthyroidism and Metso et al.3 themselves proposed a fixed dose approach by administration 259 MBq of radioiodine in patients with hyperthyroidism. In this instance, a focused analysis of mortality among patients treated with 370–740 MBq seems to be of pivotal importance. If no differences will be proved in this subgroup, the conclusion should be reformulated by underlining the differences between the administered activities and associated mortality risk.


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Luca Giovanella MD*, * Oncology Institute of Southern Switzerland, Nuclear Medicine and Thyroid Unit, Bellinzona, Switzerland.