Background: Most patients with differentiated thyroid cancer are treated with radioiodine (131-I) after thyroidectomy. The characteristics predictive of successful remnant ablation with low activities of 131-I are ill defined and could help stratify patients into those who should receive higher activities.
Methods: In a case series of 193 consecutive patients with papillary thyroid cancer who underwent total thyroidectomy and received 30 mCi (1110 MBq) of 131-I, we assessed the percentage of successful radioremnant ablation as defined by a composite of scintigraphic and biochemical endpoints. Clinical, histological, scintigraphic, and biochemical covariables were analyzed to identify associations with treatment failure.
Results: Successful radioremnant ablation with low-activity 131-I was obtained in 78% of the entire cohort of patients. The presence of limited microscopic extrathyroidal extension, nodal micrometastases, or an elevated stimulated ablation was associated with failure to ablate the remnant. While accounting for other factors in a multivariable analysis, patients with an ablation thyroglobulin of at least 6 μg/l were at a more than five times greater risk (P<0.001) to fail 30 mCi 131-I remnant ablation.
Conclusion: The majority of patients with papillary thyroid carcinoma experienced successful ablation. However, elevated-stimulated ablation thyroglobulin levels were strongly predictive of ablation failure, suggesting that this biochemical marker correlates with a more aggressive tumor profile and identifies those patients who might benefit from additional therapy.