The treatment of Graves'
hyperthyroidism (GD) complicated with
malignancy is challenging, as anti-thyroid thionamide drugs (ATDs) and anti-
cancer chemotherapy are both associated with a risk of
neutropenia. Treatment with conventional ATDs, radioactive
iodine (RAI) or
potassium iodide (KI) was attempted in 8 patients with
malignancy (34-80 years of age; 2 males and 6 females) in whom GD had been fortuitously diagnosed during a detailed systematic examination. Three patients requiring surgery were initially treated conventionally with
methylmercaptoimidazole (MMI), MMI and KI or RAI (group A; one patient each). The patients became euthyroid on days 17-31 and underwent surgery on days 25-47. RAI
therapy was administered to one patient after surgery. The patients were then treated with KI during
chemotherapy. Five other patients who did not require surgery were initially treated with 100 mg KI monotherapy (group B). The serum free T4 level declined immediately in all of these patients, and they became euthyroid on days 7-18, remaining almost entirely euthyroid for more than 120 days. Anti-
cancer chemotherapy was successfully completed for three of the patients while taking KI, despite the patients experiencing repeated episodes of anti-
cancer chemotherapy-induced
neutropenia. Our present findings suggest that, in patients with GD and
malignancy, MMI + KI or RAI may be required if immediate surgery is scheduled, but KI monotherapy may be worth trying, if anti-
cancer chemotherapy is scheduled, thus avoiding the possibility of thionamide-induced
neutropenia.