Most Frequent Type of Thyroid Cancer
Papillary thyroid cancer is the most frequent type of thyroid cancer, accounting for approximately 80% of all thyroid carcinomas. 1, 2, 3
Epidemiology of Thyroid Cancer Types
Incidence Rates
- Papillary thyroid cancer: 5.7 per 100,000 person-years
- Women: 8.8 per 100,000 woman-years
- Men: 2.7 per 100,000 man-years 1
- Follicular thyroid cancer: 0.82 per 100,000 person-years
- Women: 1.06 per 100,000 woman-years
- Men: 0.59 per 100,000 man-years 1
- Medullary thyroid cancer (MTC): 0.11 per 100,000 person-years 1
- Anaplastic thyroid cancer (ATC): 0.21 per 100,000 person-years 1
Distribution by Type
- Papillary thyroid cancer represents nearly 80-95% of all thyroid carcinomas 1, 2, 3, 4
- Follicular thyroid cancer is the second most common type
- Medullary and anaplastic thyroid cancers are rare forms
Demographic Patterns
Gender Distribution
- Thyroid cancer occurs 2-3 times more frequently in women than men 1, 5
- Among women, papillary thyroid cancer rates are highest in Asians (10.96 per 100,000 woman-years) and lowest in blacks (4.9 per 100,000 woman-years) 1, 5
- Among men, papillary thyroid cancer rates are higher in whites (3.58 per 100,000 man-years) and lower in blacks (1.56 per 100,000 man-years) 1
Age Distribution
- Peak incidence occurs around age 50 years 1
- Anaplastic thyroid cancer typically affects older patients (mean age at diagnosis ~71 years) 1
- Thyroid cancer accounts for 15.1% of all malignancies in persons aged 20-34 years 1
Trends in Thyroid Cancer Incidence
- The incidence of thyroid cancer has increased dramatically over recent decades 1
- From 1975 to 2009, thyroid cancer rates tripled, primarily due to increased detection of small papillary thyroid cancers 1
- This increase is mainly attributed to:
- Improved diagnostic techniques (ultrasound, fine needle aspiration)
- Increased detection of micropapillary carcinomas (<1 cm) 1
- 60-80% of thyroid carcinomas detected are micropapillary thyroid carcinomas 1
Clinical Significance
- Despite the high incidence of papillary thyroid cancer, it generally has an excellent prognosis
- Patients with small localized papillary thyroid cancers have a 99% survival rate at 20 years 6
- Mortality rates from thyroid cancer have decreased over the past decades despite increasing incidence 1
- Papillary thyroid cancer typically spreads to cervical lymph nodes, with distant metastases being uncommon 2
Risk Factors
- Exposure to ionizing radiation is the only established environmental risk factor for thyroid carcinoma, particularly for papillary carcinoma 1, 5
- The risk is greater in subjects exposed at younger ages 5
- Following the Chernobyl nuclear accident, there was an 80-fold increase in thyroid tumors in exposed areas 1, 5
Understanding the predominance of papillary thyroid cancer is important for clinical practice, as it influences screening approaches, diagnostic procedures, and treatment planning for patients with thyroid nodules.