Introduction

Thyroid cancer consists of a diverse group of tumours with different clinical features and prognoses. Thyroid cancer can occur at any age, but it is rare in patients under the age of 25. Radiation exposure is the best-documented risk factor. Most thyroid cancers are carcinomas: these are papillary, follicular, medullary, and anaplastic, in order of frequency. Thyroid lymphomas and sarcomas are rarer. The overall prognosis is related to histological type; well-differentiated thyroid cancer (papillary and follicular) has the best prognosis. In contrast, anaplastic carcinoma progresses rapidly and has a very poor prognosis. There is a lack of evidence from prospective randomised controlled studies because differentiated thyroid cancer is an uncommon disease with a long natural history. Many areas of thyroid cancer management remain controversial, including the extent of surgery and the indications for radioiodine ablation and radiotherapy. Evidence-based guidelines published in 2002 relied on large retrospective and cohort studies (British Thyroid Association, 2002).

This chapter focuses mainly on differentiated thyroid cancer, with shorter sections on medullary thyroid carcinoma (MTC), anaplastic thyroid cancer and thyroid lymphoma.

Types of thyroid tumour

Thyroid tumours can be divided into benign, malignant primary and malignant secondary. Types of thyroid tumour are shown in Table 35.1.

The relative proportions of patients with differentiated thyroid cancer in a geographic area depend on dietary iodine intake. The proportion of follicular cancers increases where there is dietary iodine deficiency.