Use of 131 I-MIBG Therapy in MIBG-Positive Metastatic Medullary Thyroid Carcinoma

Dear Editor:

Surgery is the most effective therapy for potential cure of medullary thyroid carcinoma (MTC), which usually consists of total thyroidectomy with a dissection of the central compartment of the neck and the jugulocarotid chains. After surgical treatment, about 50% of MTC patients are not cured. The strategies for therapy of metastatic MTC includes systemic chemotherapy, tyrosine kinase inhibitors, external radiotherapy, chemoembolization of liver metastases, and nuclear medicine procedures using ¹³¹I-meta-iodobenzylguanidine (MIBG) or ¹¹¹In-labeled somatostatin analogues. These are not well defined, however, due to the rarity of the disease. Here, we report a patient with MTC with liver metastases. The patient's history was of interest because a single dose of 150 mCi ¹³¹I-MIBG was effective against metastatic tumors and led to progressive decrease of tumor markers during a 10-year follow-up period.

In 1982, a 21-year-old woman with endocrine neoplasia type 2A presented with multifocal MTC. A total thyroidectomy with lymph node dissection was performed. There was a major increase in her serum calcitonin and carcinoembryonic antigen (CEA) levels during the next 16 years of irregular medical follow-up (see Supplementary Data, available online at www.liebertonline.com/thy). In 1998, the patient underwent neck exploration but no node metastases were diagnosed. In 1999, 17 years after surgical management, an abdominal CT scan revealed three suspicious hypervascular liver nodes. MIBG scintigraphy showed two major areas of increased uptake in liver segments III and IV and more moderate uptake in segment VII (see Supplementary Data). Liver surgery was then performed but all the metastases could not be removed. Tumor markers decreased significantly thereafter with calcitonin levels going from 5250 pg/mL before surgery to 1543 pg/mL after surgery and CEA from 419 to 79 pg/mL.

In 2000, as scintigraphy revealed significant MIBG uptake in the liver metastases, the patient was treated by a single dose of 150 mCi ¹³¹I-MIBG. Arterial phase CT scan before ¹³¹I-MIBG therapy showed two typical hypervascular liver metastases in the right lobe. Four years later, CT scan demonstrated significant mass shrinkage. The lesion in segment VIII decreased from 12 to 6 mm and the lesion in segment VI decreased from 20 to 5 mm. This partial response was confirmed 7 years later (see Supplementary Data). At the last evaluation in 2010, MIBG scintigraphy showed no pathological uptake (see Supplementary Data). We simultaneously observed a progressive and regular reduction of tumor markers with calcitonin decreasing from 1543 to 274 ng/mL (−83%) and CEA from 79 to 36 ng/mL (−55%) between 2000 and 2010, without any complementary treatment. Follow-up was uneventful with no major abnormalities in hematological indices.

Several treatment options for metastatic MTC may be considered with variable likelihood of success. Results of systemic chemotherapy are disappointing. Chemoembolization of liver metastases may be indicated to treat unresectable and symptomatic liver metastases, but data are scarce. To date, the most promising medications in patients with metastatic MTC may be tyrosine kinase inhibitors. Several of these agents have demonstrated significant partial response rates and disease stabilization, but they are not devoid of adverse effects and long-term toxicity needs to be investigated.

Our patient was treated with ¹³¹I-MIBG before the availability of tyrosine kinase inhibitors. Few data are available on use of nuclear medicine procedures in MTC. Studies have demonstrated a poor overall diagnostic accuracy of MIBG in MTC due to low sensitivity ranging from 25% to 30%, in spite of excellent specificity around 95%. Few data are available for ¹³¹I-MIBG therapy of MTC. Recently, Castellani et al. reported a series of 13 patients with MTC who received this treatment; four partial responses and four cases of stable disease were achieved. Hematological tolerance was good (1). The most frequent adverse effects of ¹³¹I-MIBG therapy for MTC are hematological, with thrombocytopenia occurring after 6 weeks. This is usually moderate and spontaneously regresses. Somatostatin analogue scintigraphy has poor diagnostic accuracy in MTC. A recent study with [⁹⁰Yttrium-DOTA]-TOC therapy in 31 patients with metastatic MTC noted a decrease in serum calcitonin in 29% of the patients (2). Anti-carcinoembryonic-antigen radioimmunotherapy has also been studied for treatment of MTC. The results of one study were promising with 9 partial responses in 19 patients, but hematological toxicity was high as 5 patients developed severe thrombocytopenia (3).

Our experience with the patient reported here indicated a beneficial potential of ¹³¹I-MIBG therapy in patients with metastatic MTC whose tumors concentrate MIBG. Currently, tyrosine kinase inhibitors seem to be emerging as a first-line treatment for metastatic (4). ¹³¹I-MIBG therapy could be an alternative in metastatic MTC patients with significant uptake of MIBG scintigraphy if tyrosine kinase inhibitors prove to be ineffective or could be indicated in patients with contra-indication to the use of tyrosine kinase inhibitors.