Second radioiodine treatment in patients with differentiated thyroid carcinoma: Causes and effects.

INTRODUCTION: Patients with incomplete response to initial therapy of thyroid cancer can be managed with ongoing observation or potentially additional therapies. Our aim was to assess the effect of a second radioactive iodine treatment (RAIT) and its relationship with causes and clinical variables.

MATERIAL AND METHODS: Patients undergoing a second RAIT for biochemical or structural incomplete response to initial therapy of DTC were retrospectively included (n=120). They were categorised based on the American Thyroid Association (ATA) classification of response to initial therapy. Patients were reclassified in the following 6-18 months after second RAIT based on imaging findings and measurements of thyroglobulin and antithyroglobulin antibody levels. The associations of a downgrading of response category and progression-free survival (PFS), and the related variables, were evaluated.

RESULTS: Sixty-six patients (55%) had a downgrading on ATA response category after second RAIT. A significant interdependence of causes for second RAIT and outcomes was found (χ2 =29.400, p=0.001), with patients with neck reoperation showing a higher rate of indeterminate or excellent responses. A significant association between ATA response to second RAIT and absence of structural progression was found (χ2 =44.914, p<0.001), with less structural progression in patients with downgrading on ATA response (χ2 =30.914, p<0.001). There was also significant interdependence to some clinical variables, such as AJCC stage (χ2 =8.460, p=0.015), ATA risk classification (χ2 =10.694, p=0.005) and initial N stage (χ2 =8.485, p=0.004).

CONCLUSIONS: In selected cases, a second RAIT could lead to more robust responses with a potential improvement in prognosis in patients with incomplete response to initial DTC treatment.