Thyroid Cancer Overview and Diagnosis

Thyroid cancer is the most common endocrine malignancy accounting for over 95% of all endocrine cancers. In 2005, according to the American Cancer Society, there were 25,690 newly diagnosed cases, accounting for 1.5% of all new cancers, and 1,490 deaths. The Surveillance, Epidemiology, and End Results (SEER) program of the National Cancer Institute estimates the prevalence of thyroid cancer as 327,000 cases in the United States, which represents less than 0.1% of the population. Thyroid cancer is increasing faster than any other cancer in the United States at a rate of 4.3% per year. Although it is increasing in all ethnic groups, white males have shown the most rapid rise in new cases. The spectrum of thyroid cancer ranges from occult papillary thyroid carcinoma, which has a relatively benign course, to very aggressive anaplastic thyroid carcinoma. Fortunately, more than 90% of all thyroid cancers are well-differentiated and individuals with these tumors have a good long-term prognosis.

The diagnosis, treatment, and follow-up for thyroid cancer is a rapidly evolving field as more sensitive imaging modalities such as ultrasound, fine needle aspiration, genetic testing, and serum markers begin playing roles. Several important techniques that have come to the forefront of diagnosis are ultrasound scanning of the neck pre- and post-operatively to evaluate and monitor the extent and persistence/recurrence of disease. Ultrasound guided fine needle aspiration (FNA) of suspicious thyroid and neck nodules for diagnosis has increased the sensitivity of cancer detection. Serum markers, thyroglobulin (TG), for well-differentiated thyroid cancer, and calcitonin and CEA, for medullary thyroid cancer, are also important and sensitive methods for detecting persistent or recurrent disease.

The extent of surgical treatment for thyroid cancer is a controversial topic. The goals of initial therapy for the management of thyroid cancer should include:

1. removal of primary tumor, disease that extends beyond the thyroid capsule, and involved cervical lymph nodes
2. minimize treatment and disease related morbidity
3. permit accurate disease staging
4. facilitate postoperative treatment with radioiodine when appropriate
5. permit accurate long-term surveillance
6. minimize the risk of recurrent local and metastatic tumor

Clinical Presentation and Diagnosis

Most thyroid cancer patients present clinically with a palpable thyroid nodule. These are usually asymptomatic. In rare cases, the patient will present with hoarseness, pain, difficulty swallowing, coughing or choking spells. In evaluating patients for thyroid cancers clinical history and physical examination remains the cornerstone of appropriate management. Important past medical history of head and neck irradiation, total body irradiation for bone marrow transplantation, exposure to fallout from Chernobyl, especially in children, a family history of thyroid cancer, and rapid growth or hoarseness. Children, men, and adults older than 60 years of age have an increased risk of malignancy. Personal and family history of other endocrine disorders, specifically, hyperparathyroidism, pituitary adenomas, pancreatic islet cell tumors, adrenal tumors, and breast cancer increase the risk of thyroid cancer. A family history of papillary or medullary carcinoma (MEN syndromes), familial polyposis, Gardner's, and Cowden's syndromes are also risk factors for thyroid cancer. High-resolution thyroid ultrasonography has become an extension of the physical examination in the evaluation of thyroid disease. Using a high frequency transducer of 10-13 MHz, nodules as small as 2mm can be detected in the thyroid.

Fine needle aspiration biopsy (FNAB) is the most reliable and cost efficient method for evaluating thyroid nodules. These should now routinely be performed under ultrasound guidance for small or difficult to palpate and/or complex nodules to reduce failure rates. Using ultrasound criteria, fine needle aspiration biopsy of the most suspicious nodules, not the largest nodules, has the highest predictive value for detecting malignancy. FNAB is not as accurate in radiation induced thyroid cancer or those with a family history of thyroid cancer, and these patients should undergo surgical resection if there is clinical suspicion of malignancy.

Preoperatively, all patients should therefore get an ultrasound examination of thyroid gland and cervical lymph nodes, as well as thyroid function tests. When differentiated thyroid cancer is suspected or proven a serum thyroglobulin, and anti-thyroglobulin antibody levels and blood calcium levels should be obtained. In the case of medullary thyroid cancer serum calcitonin, CEA, and calcium levels should be obtained. Also all patients with medullary thyroid cancer should be tested for the RET proto-oncogene and evaluated for pheochromocytoma, and hyperparathyroidism prior to surgery.