The objective of the work was to investigate the relationship between thyroglobulin doubling time (TgDT) as a marker of speed of response to 131I-therapy and the differentiated thyroid cancer (DTC) recurrence rate, DTC specific mortality rate, and relative survival rate in a DTC population followed over a long period of time after 131I-therapy. From our database, data of 1354 patients were reviewed. TgDT could be calculated in 174 patients, however, 376 patients did not have sufficient Tg values available for TgDT calculation and 804 patients reached biochemical remission before a sufficient number of Tg measurements for TgDT calculation was acquired. Main outcome measures were recurrence-free, DTC specific, and relative survival rates. In patients<45 years, TgDT in multivariate analysis was identified as the solitary significant determinant of DTC specific and relative survival. In patients≥45 years of age at diagnosis, TgDT is an independent, but not the only determinant of recurrence free, DTC specific, and relative survival. Importantly, in this age group life expectancy is normal in patients reaching rapid biochemical remission (i. e., before TgDT can be calculated); it was reduced in patients with a negative TgDT, which normally is deemed a marker of response to therapy. Only DTC patients with a rapid biochemical remission have a very good prognosis with a normal life expectancy. If no rapid biochemical remission occurs, both biochemically progressive disease and a slower biochemical remission of disease are associated with a reduced prognosis, especially in older DTC patients.
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