From the Guidelines
MIBG therapy is a recommended treatment for malignant pheochromocytoma, particularly in patients with a good uptake of 123 I-MIBG and unresectable, progressive disease, or symptomatic patients. The treatment involves administering high-dose I-131-MIBG therapy intravenously at doses ranging from 5.5 to 38 GBq (150–1000 mCi) per treatment cycle, with cycles repeated based on response and toxicity 1. Before treatment, patients require thyroid blockade with potassium iodide (SSKI) or Lugol's solution to prevent thyroid uptake of free radioiodine. Alpha and beta blockers may be needed to manage potential catecholamine release during treatment. MIBG therapy works because pheochromocytoma cells selectively take up MIBG through the same mechanisms they use for norepinephrine, allowing the attached radioactive iodine to deliver targeted radiation directly to tumor cells.
Key Considerations
- Treatment efficacy should be monitored with follow-up imaging and biochemical testing
- Common side effects include bone marrow suppression, nausea, and fatigue
- Patients must follow radiation safety precautions after treatment, including limiting close contact with others for several days
- MIBG therapy is often used in combination with other treatments such as surgery, external beam radiation, or chemotherapy for comprehensive management of malignant pheochromocytoma
Recent Guidelines
The most recent guidelines from 2020 recommend considering MIBG therapy as a first-line approach in patients with a good uptake of 123 I-MIBG and unresectable, progressive pheochromocytoma/paraganglioma or symptomatic patients 1. However, the guidelines also highlight the need for new systemic therapy options, as current treatments have limited efficacy and significant toxicity.
Treatment Outcomes
Objective responses to MIBG therapy have been observed in 22–47% of cases, with long-term survival of responders reported to be around 4.7 years or 72 months 1. However, grade 3–4 toxicity has been reported in 16%–83% of patients, highlighting the need for careful patient selection and monitoring.
Combination Therapy
MIBG therapy may be used in combination with other treatments, such as cyclophosphamide- and dacarbazine-based regimens, which have shown clinical benefits in patients with malignant pheochromocytoma 1. However, the optimal combination and sequencing of treatments require further study.
From the Research
Treatment of Malignant Pheochromocytoma with Metaiodobenzylguanidine (MIBG)
- MIBG has been used to treat malignant pheochromocytoma since the 1980s, with studies showing significant tumor responses in about 30-50% of cases 2.
- The use of low versus intermediate activity of MIBG has been compared, with results showing that intermediate single session activity can shorten the global treatment time with similar efficacy and moderate increment of toxicity 2.
- Combination of 131-I MIBG treatments and chemotherapy has been shown to produce additive effects in reducing malignant pheochromocytomas, with minimal toxicity from 131-I MIBG 3.
Efficacy of MIBG Therapy
- A comprehensive review of 116 reported patients with malignant pheochromocytoma treated with 131I-MIBG showed initial symptomatic improvement in 76% of patients, tumor responses in 30%, and hormonal responses in 45% 4.
- Patients with metastases to soft tissue had more favorable responses to treatment than those with metastases to bone 4.
- A study of 33 patients with metastatic pheochromocytoma and paraganglioma treated with 131I-MIBG showed a median survival of 4.7 years, with most patients experiencing a symptomatic response leading to improved survival 5.
Dosage and Administration
- The cumulative dose of 131I-MIBG administered ranged from 96 to 2,322 mCi (3.6 to 85.9 GBq), with a mean of 490+/-350 mCi (18.1+/-13.0 GBq) 4.
- An initial dose of 500 mCi may be optimal, with patients who received a high dose (>500 mCi) as their initial therapy showing improved survival 5.
- Adverse effects were generally mild, except for one fatality from bone marrow aplasia, and were recorded in 41% of the treated patients 4.