Cancer cells have the potential to spread from the thyroid to other parts of the body where they can grow into new tumours. This process is called metastasis. The tumours are also called metastasis (singular) or metastases (plural). Metastases are also called secondary tumours.
Understanding the usual progression of cancer helps the doctor to predict its probable course, plan treatment and anticipate further care.
The most common sites where thyroid cancer spreads depend on the type of thyroid cancer.
Papillary thyroid cancer
Papillary thyroid cancer is usually slow growing and tends to spread regionally (locally) rather than distantly.
- Regional metastasis usually occurs in the lymph nodes and soft tissues in the neck.
- The spread of cancer to the lymph nodes does not necessarily mean a poorer prognosis.
- Distant metastasis can occur in the lungs and bones, although this is rare.
Follicular thyroid cancer
Follicular thyroid cancer is slightly more aggressive than papillary thyroid cancer, although it is still considered a slow growing, well-differentiated cancer.
- It tends to spread distantly rather than regionally.
- It tends to invade the blood vessels rather than the lymph vessels.
- Distant spread occurs through the bloodstream rather than the lymphatic system.
- Distant spread usually involves the lungs or bones, although this is rare.
Anaplastic thyroid cancer
Most cases of anaplastic thyroid cancer have distant metastasis at the time of diagnosis because of the rapid growth and aggressive nature of this type of cancer.
- Common sites of metastasis include the lungs, pleura, bones and brain.
Medullary thyroid cancer
Medullary thyroid cancer commonly spreads to the regional lymph nodes in the neck.
- Distant metastasis tends to occur through the bloodstream rather than the lymphatic system.
- Distant metastasis most often occurs in the lungs, liver, adrenal glands and skin.