High-Risk Patients with Differentiated Thyroid Cancer T4 Primary Tumors Achieve Remnant Ablation Equally Well Using rhTSH or Thyroid Hormone Withdrawal

Background: Few data exist on using thyrotropin alfa (recombinant human thyroid-stimulating hormone [rhTSH]) with radioiodine for thyroid remnant ablation of patients who have T4 primary tumors (invasion beyond the thyroid capsule). Methods: A retrospective chart review protocol at nine centers in Europe was set up with special waiver of need for informed consent, along with a careful procedure to avoid selection bias when enrolling patients into the database. Data on 144 eligible patients with T4 tumors were collected (T4, N0–1, M0–1; mean age 49.7 years; 65% female; 88% papillary cancer). All had received 131I remnant ablation following TSH stimulation with rhTSH or thyroid hormone withdrawal (THW) since January 2000 (rhTSH n=74, THW n=70). The primary endpoint was based on evaluation of diagnostic radioiodine scan thyroid bed uptake more than six months after the ablation procedure, while stimulated serum Tg was a secondary endpoint. Safety was evaluated within 30 days after rhTSH or 131I. Results: Successful ablation judged by scan was achieved in 65/70 (92.9%) of rhTSH and in 61/67 (91.0%) of THW patients; the success rates were comparable, since noninferiority criteria were met. Although some patients in the initial cohort had tumor in cervical nodes and metastases, considering all evaluable patients regardless of various serum anti-Tg antibody assessments, the stimulated Tg was <2 ng/mL in 48/70 (68.6%) and 39/67 (58.2%) in rhTSH and THW groups respectively; if patients with anti-Tg antibody levels >30 IU/mL were excluded, the stimulated Tg was <2 ng/mL in 42/62 (67.7%) and 37/64 (57.8%) respectively. No serious adverse events occurred within the 30-day window after ablation. Conclusions: Use of rhTSH as preparation for thyroid remnant ablation in patients with T4 primary tumors achieved a rate of ablation success that was high and noninferior to the rate seen after THW, and rhTSH was well tolerated.