Long-term outcome of Radioiodine Therapy in Brain Metastases from Differentiated Thyroid Cancer- Single Centre Cohort Study

Objectives: Metastasis to the brain from differentiated thyroid cancer (DTC) is extremely rare. In view of the small number of published case reports or few case series, no definite modality of treatment is recommended. As the evidence on the efficacy of radioiodine therapy (RAI) is not established, the American Thyroid Association Guidelines (ATA 2015) recommends RAI therapy as an alternative treatment option when surgical excision is not feasible. The largest series published in this context was by Samuel et al. (1997) in 9 patients who were treated with RAI therapy. Hence, we share our experience of treating a relatively large number of patients with brain metastases from DTC, and the long-term outcome of the treatment, mainly by RAI and other modalities as and when required.

Methods: As an institutional policy, all patients with DTC after thyroidectomy undergo diagnostic whole body scan (Dx‐WBS) before radioiodine therapy. The post‐therapeutic scan is performed at the time of discharge to look for additional sites of disease. The patients were retreated, if required, at 6-12 month intervals after each RAI therapy cycle. All known patients with brain metastases were administered RAI under steroid cover and tapered in the next few weeks time. As per ATA 2015 guidelines response was defined as, excellent response, biochemical or structural persistent disease, recurrence, and progression based on the scintigraphic findings on Dx‐WBS, serum Tg and anti-Tg levels, structural imaging and ¹⁸F‐FDG-PET/CT as clinically indicated.

Results: On chart review of total 9218 DTC patients at our institution, from 1977 to 2018, twenty (0.2%) patients had brain metastases- 18 (90%) patients at the time of initial presentation on the first Dx-WBS or on post-therapy scan, and 2 patients developed recurrent disease on follow-up. Nineteen (95%) were females and the median age of the cohort was 54 years (range: 26 - 70 years). Total/near-total thyroidectomy with or without nodal dissection was performed in all the patients, and 3 patients underwent an additional craniotomy to remove metastases. The histopathology of the primary tumor was follicular thyroid carcinoma in 60% (12/20) and papillary carcinoma thyroid in the remaining 40 % (8/20). The median number of RAI therapy cycles administered was 4 (range 2-8) with a mean cumulative administered activity of 25.53 GBq. During the median follow-up duration of 42 months (range:10-103 months), only one patient achieved excellent response (complete morphological remission with undetectable stimulated-Tg, alive and disease-free till date, 101 months), 6 patients showed disease progression and the remaining 13 patients had a structurally incomplete response. Those who had progressive or stable structural disease were administered external beam radiotherapy alone, and currently, tyrosine kinase inhibitor therapies as well. The median time to progression was 26.5 months (95% CI: 6.3-63.3 months). The total number of deaths, recorded during the course of follow-up was 15 (75%) patients. The median overall survival duration was 38 months (95% CI: 28-98 months). We observed that the prognosis of brain metastases from DTC is dismal (75% death recorded till date). However, the median overall survival duration was 38 months, much longer than reported in the literature (12 months).

Conclusions: We conclude, if brain metastases show avid radioiodine uptake, RAI therapy should be offered before EBRT or surgery.