The value of detectable thyroglobulin in patients with differentiated thyroid cancer after initial 131I therapy

Objective To assess the prognostic value of detectable thyroglobulin (Tg) after initial surgery and radioactive iodine (I-131) therapy by comparing patients with a negative post-therapeutic whole body scan (WBS) with either detectable or undetectable Tg. Background Differentiated thyroid cancer has a good prognosis. However, recurrences can occur up to 30 years after initial treatment. Because life-long follow-up is necessary, it is important to explore possible risk factors associated with recurrence and mortality. Design, patients and measurements We studied 539 patients who were treated between 1980 and 2007. After the last therapeutic dosage of 5550 MBq I-131, 72 patients had negative post-therapeutic WBS and positive Tg levels (Tg+ group) and 399 patients had negative post-therapeutic WBS and negative Tg (Tg- group). The 68 remaining patients had proven residual macroscopic disease. We investigated recurrences and overall mortality in the Tg+ and Tg- group compared with the Dutch population. Results In the Tg+ group, detectable recurrences occurred significantly earlier and more frequently than in the Tg- group (19% vs 13%, P = 0.024). Survival between these groups was comparable, but shorter than the general Dutch population [Standardised Mortality Rate (SMR) 1.38 (95% CI 1.12; 1.63) (P = 0.003)]. Disease-free survival in the Tg groups was comparable and not significantly different from the Dutch population [SMR = 1.09 (95% CI 0.81; 1.34) (P = 0.569)]. Conclusion Patients with detectable Tg during the last I-131 treatment and a negative post-therapeutic WBS have significant earlier and more recurrences than patients without detectable Tg. Survival in both groups is comparable. After initial therapy, the combination of a negative high dose post-therapeutic WBS with detectable Tg is a valuable predictor for earlier and more recurrences, but is not associated with survival.