Somatostatin Receptor Scintigraphy as a Potential Diagnostic and Treatment Modality for Thyroid Follicular-Cell-Derived Cancers

Dear Editor:

Differentiated thyroid carcinoma is a common malignancy with several well-known treatment stratagems. There are also well-established imaging modalities commonly used for both the diagnosis and surveillance of this malignancy. Despite these vast advances, however, there remain cases that are both difficult to detect and treat.

The incidental detection of nonmedullary thyroid carcinoma by somatostatin receptor scintigraphy (SRS) is a known phenomenon. Additionally, the presence of somatostatin (SST) receptors, and the growth regulatory effects of SST itself on tumoral thyroid cells have been documented in a small number of in vitro studies. Most recently, a study was published in Thyroid showing increased indium-111 (In-111) uptake beyond the usual basal activity in cases of Hashimoto's thyroiditis, nodular thyroids, and hot nodules (1). The full meaning of these findings and the possible implications for treatment of thyroid cancer are not well defined. Herein we report a 73-year-old man with appendiceal carcinoid and Hürthle-cell-type follicular carcinoma of the thyroid, found during routine surveillance with In-111 octreotide scintigraphy. This patient highlights the potential use of SRS in the diagnosis and evaluation of follicular-cell-derived thyroid cancer and invites speculation about implications for therapy.

Our patient was found to have appendiceal carcinoid in the setting of surgery for acute appendicitis. He underwent his first routine surveillance for metastases with SRS several months after surgery. The imaging revealed a focus of avid In-111 activity in the right side of the neck (Fig. 1). Both subsequent ultrasonography and computed tomography scan of the neck revealed a 2.8 × 1.8 × 3.5 cm lesion in the right thyroid lobe of a multinodular goiter. Ultrasound-guided fine-needle biopsy of the lesion was suggestive of a thyroid follicular neoplasm. The patient was euthyroid and free of antithyroid antibodies. Total thyroidectomy was performed and pathology revealed a 3-cm follicular Hürthle cell carcinoma, with angiolymphatic invasion. The tumor cells were positive on immunohistochemical staining for thyroglobulin, synaptophysin, and thyroid transcription factor-1 (TTF-1), but negative for calcitonin and chromogranin. After total thyroidectomy was performed, SRS, ultrasonography, post-I¹³¹ whole-body scan, positron emission tomography/computed tomography, and stimulated thyroglobulin assay all revealed no evidence of cancer.

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FIG. 1.

Preoperative Octreoscan^®.

In-111 octreotide is a radiopharmaceutical that binds to and images neuroendocrine tumors with SST receptors. The false-positive rate reportedly is 3/508 (2). In the patient presented here In-111 SRS revealed a Hürthle cell follicular thyroid cancer.

Ligand binding to SST receptors has been shown in vitro with both normal thyroid and nonmedullary thyroid cancer cell lines (2). The functionality of these receptors has also been demonstrated by positive growth response to SST analogs, predominantly types 3 and 5 (2). Currently available analogs, such as those utilized by In-111 pentetreotide scintigraphy and the newer Gallium-68 DOTA-Phe(I)-Tyr(3)-octreotide (DOTATOC) positron emission tomography, act mainly on subtype 2 (1).

With regard to mechanism of action, in vitro studies have demonstrated an inhibitory effect of SST on thyrotropin-induced thyrocyte proliferation, incorporation of 3H-thymidine into RNA of follicular cells, and thyrotropin-stimulated adenylate cyclase activity in tumoral thyroid tissue (3,4). Further, an antiproliferative effect on nonmedullary thyroid cancer cells has also been shown (4).

Clinical studies of the use of SRS in the evaluation of nonmedullary thyroid cancer are limited. There is evidence that suggests that SRS may be a useful imaging tool in thyroid cancer, especially in nonradioiodine-accumulating cancer of the Hürthle cell variety. Our patient may encourage new studies to evaluate this novel use for SRS.

Clinical studies looking at the use of available SST analogs have failed to show therapeutic benefit for thyroid cancer. Perhaps new SST analogs, such as SOM230 (Pasireotide), with higher binding affinities for different subtypes of SST receptors may offer a fresh opportunity to revisit the treatment of Hürthle cell thyroid cancer.