FDG-PET in Thyroid Cancer

Diagnostic Procedures in the Follow-Up of Patients Affected by Men Type 2

Multiple endocrine neoplasia type 2 (MEN 2) is an inherited disease caused by germline mutations in the RET proto-oncogene. The most distinctive MEN 2 variants are MEN 2A, MEN 2B and familial medullary thyroid cancer (FMTC). The hallmark of these syndromes is the development of medullary thyroid carcinoma (MTC), which occurs in almost all patients with MEN 2 syndromes. Other endocrinopathies are variably expressed. Pheochromocytoma and hyperparathyroidism occur in patients with MEN 2A with a frequency of about 50% and 30%, respectively. In this paper we summarize the most relevant diagnostic methods to detect and monitor MTC, pheochromocytoma and hyperparathyroidism.

PET/CT in Neuroendocrine Tumors: Evaluation of Receptor Status and Metabolism

In-111 Octreoscan is considered the gold standard for imaging of neuroendocrine tumors (NET). However, in the absence of morphologic imaging correlation, the exact localisation of the tumor is often difficult. Also the sensitivity of PET imaging is more than Gamma camera (SPECT) imaging. Ga-68 labelled somatostatin analogs (SMS-R) are interesting radiopharmaceuticals for PET receptor imaging of NET. Some other radiopharmaceuticals e.g. F-18 DOPA can also be used to assess metabolism and functional status of NET. The importance of these radiopharmaceuticals, especially SMS-R increases in the absence of any specific biochemical marker or clinical parameter for follow-up of patients after therapy (eg peptide receptor radionuclide therapy, surgery, chemoembolisation, etc). New criteria based on molecular, metabolic and morphologic imaging needs to be developed for correct assessment of response to therapy for these slow-growing, solid tumors.

External beam radiation therapy for thyroid cancer

This article discusses the role of external beam radiotherapy (XRT) in the management of well-differentiated thyroid cancer (WDTC), medullary thyroid cancer, and anaplastic thyroid cancer. Although there are no randomized controlled studies on the use of XRT in thyroid cancer, evidence supports its use to treat gross disease after surgery or unresectable cancer and its use as an adjuvant after resection of a known high-risk disease in WDTC, and, to a lesser extent, in medullary thyroid cancer. The use of XRT for the palliation of symptomatic disease and recent advances in the technology of radiation delivery also will be discussed.

Detection of occult medullary thyroid cancer recurrence with 2-deoxy-2-[F-18]fluoro-D-glucose-PET and PET/CT

PURPOSE

2-deoxy-2-[F-18]fluoro-D-glucose (FDG)-positron emission tomography (PET) has an established role in restaging of various cancers, including papillary and undifferentiated thyroid carcinoma. However, controversies exist regarding its ability to reliably assess recurrent medullary thyroid cancer (MTC). We were therefore prompted to review our experience with FDG-PET for detection of occult MTC.

METHODS

This is a retrospective study (Apr 1, 1997-Mar 31, 2004) of 13 patients with histologic diagnosis of MTC, who had PET examinations. The group included six men and seven women, 15-62 years old (average: 48+/-13). The PET scan request was triggered by rising levels of calcitonin and negative anatomical imaging studies.

RESULTS

Recurrent/metastatic disease was identified by PET in seven (54%) of the 13 patients. The lesions were located in superior mediastinum (4), cervical lymph nodes (3), thyroid bed (2), lung (1) and liver (1). The calcitonin levels ranged from 52 to 5,090 pg/ml (average: 1,996 pg/ml) in patients with negative PET scans and from 132 to 9,500 pg/ml (average: 3,757 pg/ml) in patients with positive studies. The sensitivity and specificity of FDG-PET for disease detection in this cohort were 85.7% (95% CI: 48.7-97.4) and 83.3% (95% CI: 43.6-96.9), respectively.

CONCLUSION

Our findings suggest a significant role for FDG-PET in patients with suspected MTC recurrence, with sensitivity of 85.7% and specificity of 83.3% for disease detection. FDG-PET provides additional information in a significant fraction of cases (54%) and could be used for restaging of patients with MTC and elevated levels of biomarkers (calcitonin). Additional studies are necessary to further evaluate the role of FDG-PET in MTC.