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

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.

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.

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).

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.