Survival Analysis of 19 Patients with Toxic Thyroid Carcinoma

Among patients with differentiated thyroid carcinoma (diffTCa), the rare hyperfunctioning or toxic TCa (ToxTCa) was diagnosed when scintigraphic hot thyroid areas were attributable only to diffTCa (diameter >1 cm by pathological examination) and/or total thyroidectomy failed to induce hypothyroidism. Of 924 cases of all TCa (papillary diffTCa 47.3%, follicular diffTCa 44.2%, others 8.5%), 19 had ToxTCa (2.1%, 15 of 19 follicular, 4 of 19 papillary, P = 0.008). These received a more intensive radioiodine therapy (average cumulated 131I activities 21.8 vs. 15.2 GBq, P < 0.01). Five-year survival rates for ToxTCa (n = 19, 56%) and diffTCa (n = 545, 94.5%) differed [hazard ratio 4.8, 95% confidence interval (CI) 2.8–8.1, P = 0.001]. However, the differences were attenuated by matching ToxTCa and diffTCa (n = 57, 5-yr survival rate 74%) for age, sex, and histopathologic type (hazard ratio 2.1, 95% CI 1.13–3.9, P = 0.02). Correcting statistically for M1 against M0 stage distribution resulted in a further reduction of the hazard ratio (hazard ratio 1.8, 95% CI 0.93–3.48, P = 0.08). An M1 stage is an important prognostic factor in ToxTCa patients. Thus, ToxTCa, treated with higher activities of 131I, has a survival prognosis close to that of matched diffTCa cases, both groups consisting mainly (79%) of follicular subtypes.