Digoxin for the Reinduction of Radioiodine Uptake in Metastatic or Locally Advanced Non-medullary Thyroid Carcinoma

Inclusion Criteria:

* Non-medullary thyroid carcinoma
* Having undergone total thyroidectomy and at least 1 treatment with \[131\]sodium iodine (NaI)
* Presence of local or metastatic disease, radiologically proven. A minimum of 1 target lesion (at least 1cm for soft tissue and 1.5cm for lymph nodes) must be present.
* Radioiodine refractory disease; at least one lesion without therapeutic relevant uptake at previous post-therapeutic scintigraphy and/or negative diagnostic \[123\]NaI-scan.
* The target lesion must not be eligible for local treatments.
* Hematologic lab values should be at least: absolute neutrophil count \>1.4x10\^9/liter, hemoglobin\>5.5mmol/liter, thrombocytes \>99x10\^9/liter

Exclusion Criteria:

* Creatinine clearance \<50ml/min and/or active kidney disease
* Cardiac arrhythmias
* Electrolyte disorder
* Concomitant drugs that interfere with digoxin metabolism such as P-glycoprotein inductors or inducers, including but not limited to penicillamine, sulfasalazin, tipranavir, amiodarona, diltiazem, itraconazole, ketoconazole, kinidin, lapatinib, propafenon, vemurafenib, verapamil, azithromycin, clarithromycin, erythromycin, roxithromycin, chloroquin, ciclosporin, anti hepatitis C drugs, anti-HIV drugs, hydroxychloroquine.
* Pregnancy, lactating or breast-feeding women.
* Having undergone a procedure with iodine contrast agent within the last 3 months.
* Prior therapy with radioactive iodine \<6 months prior to participation.
* External beam radiation therapy \<4 weeks prior to participation.
* Having undergone chemotherapy or targeted therapy \<4 weeks prior to participation.
* Eastern Cooperative Oncology Group (ECOG) score \>2.
* Use of other investigational drugs within 4 weeks preceding the first dose of digoxin treatment.
* Known immediate or delayed hypersensitivity reaction or idiosyncrasy to drugs chemically related to digoxin.
* Uncontrolled intercurrent illness that would limit compliance with the study requirements.
* Unwillingness or inability to comply with study and follow-up procedures.
* Other active malignancies other than basal cell carcinoma. Malignancies that have been in complete remission over 2 years are not considered active malignancies.
* Rapidly progressive disease in which urgent start with systemic therapy is required.