Radioisotope therapy slowed metastatic pheochromocytoma, paraganglioma


AT ENDO 2013

SAN FRANCISCO – A majority of 22 patients with metastatic, inoperable pheochromocytoma or paraganglioma had stable disease or complete resolution 6 months after receiving the first dose of treatment with the radioisotope 131I-meta-iodobenzylguanidine.

Treatment with 131I-meta-iodobenzylguanidine (131I-MIBG) appears to be safe and was associated with disease stabilization or improvement, which makes it a useful therapeutic tool either alone or with external beam radiotherapy and chemotherapy for patients with metastatic pheochromocytoma or paraganglioma, according to Dr. Matthew A. Rutherford of Glasgow (Scotland) Royal Infirmary and his associates.

In general, approximately 10% of cases of pheochromocytoma and paraganglioma metastasize. Optimal treatment of these cases has been controversial as the tumors are rare and there is no standard therapy.

The researchers reviewed the experience of one tertiary center in offering treatment with 131I-MIBG from 1986 to 2011.

The 12 patients with metastatic pheochromocytoma and 10 patients with metastatic paraganglioma received a total of 68 doses of 131I-MIBG, a type of radioactive iodine. The average dose was 9,835 MBq (range, 5,000-11,300).

One year after starting therapy, 16 of the 22 patients were alive. The average survival time after the first dose of 131I-MIBG was more than 7 years (86 months), Dr. Rutherford reported in a featured poster presentation at the Endocrine Society’s Annual Meeting.

At the 6-month follow-up after starting 131I-MIBG treatment, one patient had complete resolution of disease as assessed by symptoms, biochemical assessment of catecholamine excretion rate, and tumor size, Dr. Rutherford reported.

Four patients (18%) had partial responses in symptoms. A partial biochemical or tumor response, defined as greater than a 50% reduction in catecholamine excretion rate or tumor bulk, was seen in one patient (5%) biochemically and three patients (14%) by tumor size.

Stable disease was defined as no change in symptoms, biochemical markers, or tumor bulk, or less than a 25% increase in tumor bulk or catecholamine excretion rate. Thirteen patients had stable symptoms, 11 had stable biochemical results, and 13 had stable tumor size.

Progressive disease was identified by increased symptoms in two patients, by a greater than a 25% increase in catecholamine excretion rate in two patients, and by a greater than 50% increase in tumor size in two patients. There were no 6-month data for two patients regarding symptoms, for seven patients regarding biochemical assessment, and for three patients regarding tumor bulk.

Eleven (50%) reported having no adverse effects from 131I-MIBG, seven (32%) had nausea and vomiting, and five (23%) developed transient bone marrow defects. There were no severe adverse events related to treatment.

Fourteen patients had no treatment other than 131I-MIBG (64%), while five patients also underwent chemotherapy, one had radiotherapy, and two patients underwent chemoradiotherapy.

Bone was the most common site of metastasis (nine patients), followed by lymph nodes (eight patients) and liver (five patients), with local invasion in two patients.

The patients’ mean age was 45 years (range, 15-77 years). Nine of the 22 were male. They were followed according to a defined protocol, with repeat hormonal evaluation and imaging within 6 months of starting 131I-MIBG treatment when possible.

Genetic testing identified four patients who were positive for the succinate dehydrogenase B gene (SDHB) and four with no identified genetic mutation. The other 14 patients were not tested for genetic mutations; 7 of them were older than the institution’s age cut-off for routine genetic testing.

Dr. Rutherford reported having no financial disclosures.

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