A new treatment modality for inoperable or metastasized gastroenteropancreatic
tumors is the use of radiolabeled
somatostatin analogs. Initial studies with high doses of [(111)In-diethylenetriaminepentaacetic
acid (
DTPA)(0)]
octreotide in patients with metastasized
neuroendocrine tumors were encouraging, although partial remissions were uncommon. Another radiolabeled
somatostatin analog that is used for
peptide receptor radionuclide therapy (PRRT) is [(90)Y-1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic
acid (
DOTA)(0),
Tyr(3)]octreotide. Various phase 1 and phase 2 PRRT trials have been performed with this compound. Despite differences in the protocols used, complete and partial remissions in most of the studies with [(90)
Y-DOTA(0),
Tyr(3)]octreotide were in the same ranges, 10%-30%; these ranges were higher than those obtained with [(111)In-
DTPA(0)]
octreotide. Treatment with the newest radiolabeled
somatostatin analog, [(177)Lu-
DOTA(0),
Tyr(3)]octreotate, which has a higher affinity for the subtype 2
somatostatin receptor, resulted in complete or partial remissions in 30% of 76 patients.
Tumor regression was positively correlated with a high level of uptake on
OctreoScan imaging, a limited hepatic
tumor mass, and a high Karnofsky performance score. Treatment with radiolabeled
somatostatin analogs is a promising new tool in the management of patients with inoperable or metastasized
neuroendocrine tumors. Symptomatic improvement may occur with all (111)In-, (90)Y-, or (177)Lu-labeled
somatostatin analogs that have been used for PRRT. The results obtained with [(90)
Y-DOTA(0),
Tyr(3)]octreotide and [(177)Lu-
DOTA(0),
Tyr(3)]octreotate are very encouraging in terms of
tumor regression. Also, if kidney
protective agents are used, the side effects of this
therapy are few and mild, and the duration of the
therapy response for both
radiopharmaceuticals is more than 2 y. These data compare favorably with those for the limited number of alternative treatment approaches.