Thyroid Cancer

Abstract

• Thyroid cancer occurs in less than 1% of the population. Benign nodules are far more common, found in 19–67% of randomly selected individuals, with a higher frequency in women and the elderly.

• Thyroid cancer is more common in women, but mortality is higher in men.

• Differentiated, medullary, and anaplastic are the three main types of thyroid cancer. The differentiated histologies are classified as papillary, follicular, and Hürthle cell.

• Papillary thyroid carcinoma is the most favorable differentiated histology, followed by follicular and then Hürthle cell carcinoma.

• Differentiated histologies are the most common (90%). Of these, papillary carcinomas comprise 85%; follicular, 10%; and Hürthle cell carcinoma, 3%.

• Anaplastic carcinomas represent only 2% of cases.

• Surgery and adjuvant ¹³¹I are the mainstays of treatment for papillary and follicular variants. Iodine imaging should be performed for all differentiated variants, although Hürthle cell carcinoma is avid only 25% of the time.

• ¹³¹I typically delivers a dose of 80 Gy to the thyroid remnant or residual disease, for iodine avid tumors, when given therapeutically. When given for remnant ablation, the delivered dose is roughly 30 Gy.

• Fine-needle aspiration (FNA) is accurate for papillary and medullary carcinoma, but more tissue is required to diagnose follicular and anaplastic histologies.

• Medullary carcinoma is associated with multiple endocrine neoplasia and other familial syndromes (multiple endocrine neoplasia [MEN] 2A and 2B and familial medullary thyroid cancer [FMTC]), although 80% of cases are sporadic.

• Medullary thyroid cancer tends to progress indolently, but it is difficult to control.

• Anaplastic thyroid carcinoma is usually fatal and takes a rapid course. However, aggressive locoregional management is indicated to avoid airway compromise.

• No prospective randomized trials have been performed to evaluate the role of external-beam radiotherapy.