Just 5%-10% of thyroid nodules turn out to be malignant. Malignant (cancerous)
tumors are able to spread into nearby tissues and can travel via the
bloodstream to other parts of the body and create tumors at those sites. This
long distance travel and colonization is called metastasizing.
There are four major types of thyroid cancer: papillary,
follicular, medullary, and anplastic. The doctors are able to differentiate
between them by the way that they look under the microscope and their growth
patterns.
Papillary Tumors
Papillary cancer, also known as papillary carcinoma or papillary
adenocarcinoma, are usually very slow-growing and develop from the thyroid
follicle cells. The cancerous cells appear as tiny mushroom-shaped patterns in
the tumor.
Papillary tumors sometimes involve both lobes, but are most often found in
only one lobe. There are several different subtypes of this carcinoma
(cancer). Despite its slow growth, it can quickly spread into the lymph
nodes (bean sized collections of infection-fighting white cells) of the
neck. Even so, the prognosis for this most common form of thyroid cancer is
usually good.
Follicular Thyroid Cancer
This is the second most common type of thyroid cancer. It is also known as follicular
carcinoma or follicular adenocarcinoma. These tumors are surrounded
by a thin layer of tissue called a capsule and are more common in
countries with widespread iodine deficiencies in their diets. This form of
thyroid cancer tends to stay in the gland but do sometimes spread to areas such
as the lungs and bones.
The follicular cancer spreads to the lymph nodes less than the papillary
type, but the prognosis tends to be the about the same or slightly worse.