PubMed2000
The optimal treatment of metastatic thyroid cancer that produces high amounts of thyroid hormone has not been well defined. A 46-yr-old woman presented with a follicular thyroid carcinoma arising from a struma ovarii with hepatic metastases. After the removal of both the struma and the thyroid gland, the liver metastases showed evidence of a high degree of hormonogenesis. Brain, chest, abdomen, and bone imaging was negative for additional metastases. Because iodine uptake by most thyroid carcinomas is quite low in the absence of high levels of ambient TSH, we used recombinant human TSH (rhTSH) (Thyrogen) to achieve a concentration of 131I activity in the tumor high enough for a significant cytotoxic effect. After rhTSH administration (0.9 mg im daily for 2 consecutive days), a 131I diagnostic whole body scan confirmed the existence of 17 discrete hepatic foci of 131I uptake. To calculate the amount of 131I that would deliver an absorbed radiation dose that would be optimally cytotoxic to the metastases (>8000 rad/lesion) and not to the normal liver, we performed lesion dosimetry. Analysis of dosimetric data showed that 15 of 17 lesions would receive an adequate radiation dose following the administration of 65 mCi of 131I. Additionally, we performed whole body dosimetry to assure that this dose would not cause bone marrow toxicity. The patient was reevaluated 6 months after therapy; the liver metastases showed significant, but partial, response. In conclusion, we used the combination of rhTSH with lesional and whole body dosimetry for the treatment of highly functional metastases from follicular thyroid carcinoma arising within a struma ovarii. This strategy can be applied to determine a safe and effective dose of 131I for the treatment of any thyroid cancer metastases that produce enough TH to preclude stimulation of endogenous pituitary TSH secretion.