What is the most frequent type of thyroid cancer?

Papillary Thyroid Cancer is the Most Frequent Type of Thyroid Cancer

Papillary thyroid cancer is by far the most common type of thyroid cancer, accounting for approximately 89% of all thyroid cancer cases. 1

Epidemiology of Thyroid Cancer Types

Thyroid cancer is the most common endocrine malignancy, representing less than 1% of all human tumors. The distribution of thyroid cancer types shows a clear predominance of papillary thyroid cancer:

• Papillary thyroid carcinoma: 89% of cases 1
• Follicular thyroid carcinoma: 5.1% of cases 1
• Hürthle cell carcinoma: 2.2% of cases 1
• Medullary thyroid carcinoma: 1.7% of cases 1
• Anaplastic thyroid carcinoma: 0.8% of cases 1

This distribution is supported by earlier data showing that among 53,856 patients treated for thyroid carcinoma between 1985 and 1995,80% had papillary carcinoma, 11% had follicular carcinoma, 3% had Hürthle cell carcinoma, 4% had medullary carcinoma, and 2% had anaplastic thyroid carcinoma 1.

Incidence Trends

The incidence of thyroid cancer has been increasing worldwide over recent decades, with this increase primarily attributed to papillary thyroid cancer:

• The annual incidence of papillary thyroid cancer in the USA is 5.7 per 100,000 person-years (8.8 per 100,000 woman-years and 2.7 per 100,000 man-years) 1
• Incidence rates for papillary thyroid cancer vary by ethnicity, with higher rates among Asian women (10.96 per 100,000 woman-years) and lower rates among black women (4.9 per 100,000 woman-years) 1
• In contrast, the incidence of other thyroid cancer types (follicular, medullary, and anaplastic) has remained relatively stable 1

Characteristics of Papillary Thyroid Cancer

Papillary thyroid cancer has several distinctive features:

• It is typically indolent with an excellent prognosis (10-year survival generally exceeds 90%) 2
• The 5-year relative survival rate for patients with papillary thyroid carcinoma (stages I-III) is approximately 98% 1
• Micropapillary thyroid carcinomas (<1 cm in size) account for 60-80% of thyroid carcinomas detected today 1
• The increase in incidence is partly attributed to improved diagnostic techniques, particularly neck ultrasound and fine needle aspiration cytology 1

Risk Factors

Several risk factors have been associated with papillary thyroid cancer:

• Exposure to ionizing radiation, particularly at a young age 1
• Iodine deficiency 2
• Family history of thyroid cancer 2
• Female gender (thyroid cancer occurs 2-3 times more often in women than men) 1

Clinical Significance

Understanding that papillary thyroid cancer is the most common type has important clinical implications:

• Most thyroid cancer management protocols are primarily designed for papillary thyroid cancer
• The generally favorable prognosis of papillary thyroid cancer explains the overall good survival rates for thyroid cancer despite increasing incidence
• The high proportion of micropapillary carcinomas contributes to the debate about potential overdiagnosis and overtreatment of small, indolent tumors

Despite being the most common type, it's important to recognize that certain variants of papillary thyroid cancer can exhibit more aggressive behavior, which significantly increases the risk of postoperative recurrence 3.