Diagnosing Pediatric Thyroid Cancer: Laboratory Studies

• Thyroglossal duct cysts, the most common developmental thyroid anomaly, carry an increased, albeit small, risk of malignant transformation. This is one of the reasons excision with the Sistrunk procedure (removal of cyst, central hyoid bone, and core from the base of the tongue) is recommended. However, only 8 cases of malignant thyroglossal duct transformation have been reported in the literature.

• Levels of serum triiodothyronine (T3), thyroxine (T4), and thyroid-stimulating hormone (TSH) are usually within reference ranges in malignancy. Therefore, although these blood studies have no predictive value for thyroid cancer, they help shape the differential diagnosis of a child's thyroid mass.

• Antithyroid antibodies are helpful in diagnosing chronic lymphocytic thyroiditis. Thyroglobulin levels may be elevated in differentiated thyroid carcinoma and may help in postoperative monitoring. The thyroglobulin level should not be measured until at least 14 days after fine-needle aspiration (FNA) to prevent an artificial level elevation from the needle instrumentation.

• Traditional screening for both medullary thyroid cancer (MTC) and thyroid C-cell hyperplasia is performed by measuring calcitonin levels before and after pentagastrin stimulation. Screening for multiple endocrine neoplasia 2 (MEN2) is now possible with DNA analysis for specific mutations in the ret protooncogene.

• Serum carcinoembryonic antigen (CEA) should be measured in those in whom MTC is suspected. Unfortunately, a negative value may be found in advanced stages of the disease.

• Obtain a 24-hour urine collection to screen for catecholamines metabolites, as a pheochromocytoma or paraganglioma should be surgically removed before thyroidectomy to avoid a hypertension crisis during surgery.

• Obtain genetic testing at birth in children at risk for MEN2B and no later than age one year in children at risk for MEN2A.

Author: Mark E Gerber, MD, FACS, FAAP  Clinical Assistant Professor of Otolaryngology, University of Chicago, Pritzker School of Medicine; Section Head, Pediatric Otolaryngology-Head and Neck Surgery, NorthShore University HealthSystem  

Co-Author: Brian Kip Reilly, MD  Assistant Professor of Otolaryngology and Pediatrics, Department of Otolaryngology, Children's National Medical Center, George Washington University School of Medicine