Understanding Cancer Aggressiveness
Thyroid cancer originates in the thyroid, a butterfly-shaped gland at the base of the neck that produces hormones regulating metabolism, heart rate, and body temperature.
Cancer aggressiveness describes how a cancer behaves. This includes the speed at which cancer cells grow and multiply, their likelihood of spreading (locally, regionally, or distantly), and the difficulty of treatment.
Types of Thyroid Cancer and Their Characteristics
Thyroid cancer presents in several forms, each with distinct characteristics regarding growth and spread.
Papillary thyroid carcinoma (PTC) is the most common type, accounting for about 80% of all thyroid cancers. It typically grows slowly and often spreads to lymph nodes in the neck. Despite lymphatic spread, papillary cancer is rarely fatal and generally has an excellent prognosis. It frequently affects individuals between 30 and 50 years of age.
Follicular thyroid carcinoma (FTC) is the second most common type, making up about 10% to 15% of diagnoses. While it can spread to lymph nodes, this is less common than with papillary cancer. Follicular cancer is more prone to spreading through the bloodstream to distant sites, such as the lungs and bones. It is considered slightly more aggressive than papillary thyroid cancer and often affects individuals between 40 and 60 years old.
Medullary thyroid carcinoma (MTC) accounts for less than 5% of all thyroid cancers. It originates from the parafollicular C cells of the thyroid gland, which produce the hormone calcitonin. MTC can occur sporadically or be inherited, often linked to mutations in the RET gene. This type is considered intermediate in aggressiveness and can spread to lymph nodes, lungs, liver, and bones.
Anaplastic thyroid carcinoma (ATC) is a rare but highly aggressive form of thyroid cancer, comprising about 2% to 3% of cases. It is characterized by rapid growth and a tendency to spread quickly to nearby tissues and distant organs. Anaplastic cancer is challenging to treat and generally has a poor prognosis. It typically affects individuals over 60 years of age.
Factors Influencing Thyroid Cancer Behavior
Several factors beyond the specific type of thyroid cancer can influence its behavior and a patient’s outlook.
A patient’s age at diagnosis plays a role in prognosis. For differentiated thyroid cancers like papillary and follicular types, younger patients, particularly those under 55 years old, often have a more favorable prognosis. Older age at diagnosis can be associated with less favorable outcomes.
Tumor size also impacts prognosis. Larger tumors are associated with a less favorable outlook. While lymph node involvement is common, especially with papillary thyroid cancer, it does not always significantly worsen the long-term outlook for differentiated types. However, distant metastases, where the cancer has spread to organs far from the thyroid, significantly lower survival rates. Common sites for distant spread include the lungs and bones.
Specific genetic mutations can also affect thyroid cancer’s behavior. Mutations in genes such as BRAF, RAS, RET, and TERT promoter can be associated with more aggressive forms and poorer outcomes. For instance, the coexistence of BRAF with TERT promoter mutations in papillary thyroid cancer has been linked to larger tumors, spread to surrounding tissue, and a higher risk of recurrence.
Overall Outlook for Thyroid Cancer
The overall outlook for thyroid cancer is generally positive, particularly for the more common types. Most thyroid cancers are highly treatable, and patients often experience excellent long-term survival rates.
For localized thyroid cancer, meaning it has not spread outside the thyroid, the 5-year survival rate is nearly 100%. When the cancer has spread to nearby lymph nodes (regional spread), the 5-year survival rate remains high, at approximately 98.3%.
Even when differentiated thyroid cancer has spread to distant parts of the body, the 5-year survival rate is around 53.5%, though this can vary depending on the extent of spread. For anaplastic thyroid cancer, the prognosis is considerably different due to its aggressive nature, with a 5-year survival rate of about 7%. Early detection and appropriate treatment are important for achieving positive outcomes.