Background and aim: 111In-DTPA-octreotide is internalized by thyroid and neuroendocrine cancer cells via somatostatin receptor subtypes and can cause DNA damage by the emission of conversion and Auger electrons. The aim of the study was to determine the effect of 111In-DTPA-octreotide therapy in patients with progressive radioiodine non-responsive thyroid cancer in relation to 111In-DTPA-octreotide uptake by tumour localizations assessed on pre-treatment diagnostic octreotide scans.
Methods: Eleven consecutive patients, selected on positive pretreatment diagnostic scans, were treated with fixed doses of approx. 7400 MBq of 111In-DTPA-octreotide with an interval of 2-3 weeks between the doses. In one patient, the dose was adjusted because of sickle-cell disease. To assess the effects during treatment with 111In-DTPA-octreotide thyroglobulin levels were gathered from 2 years before treatment, during treatment and up to 1 year after treatment. A computed tomography scan was performed 3 months after the last treatment.
Results: Two patients died during and shortly after the treatment course. Death was due to a sepsis and an insulin overdose, respectively. In 44% of the patients, stable disease was achieved up to 6 months after the first treatment according to both criteria. All four had relative low pretreatment thyroglobulin values (mean value 275 microg.l), representing limited metastasized disease. In two patients biochemical stable disease was observed, whereas computed tomography showed tumour progression.
Conclusion: Treatment with high doses of 111In-DTPA-octreotide in differentiated thyroid cancer results in a stable disease in a subgroup of patients. Our results suggest that a low pre-treatment thyroglobulin value, representing a small tumour load, may be a selection criterion for treatment.