Rehnquist is 80 years old. He has been a member of the U.S. Supreme Court since 1972, serving as chief justice since 1986.

What Is Thyroid Cancer?

There are about 18,000 cases of thyroid cancer annually in the U.S. (13,000 women and 4,600 men), accounting for about 1.1% of all cancer cases and about 1,200 deaths a year.

Most patients are cured of their disease or live many years with the disease.

The thyroid gland -- located in the lower front of the neck at the base of the throat -- has two lobes. The thyroid gland makes two important hormones that help the body function.

Thyroid cancers are usually found when a bump is seen in the neck. A biopsy will determine whether the nodule (bump) contains cancer. Only about 5%-10% of nodules are cancerous.

More Information on Thyroid Cancers

There are four main types of thyroid cancer:

Papillary

Follicular

Medullary

Anaplastic

Details about Rehnquist's type of thyroid cancer have not been made available.

The majority of thyroid cancers are either papillary or follicular cancers. These are commonly called well-differentiated cancers. Both medullary and anaplastic are undifferentiated, a more aggressive type of cancer.

Aggressive Thyroid Cancers

Medullary thyroid cancer is uncommon -- accounting for about 5% of all thyroid cancers. Unlike other types of thyroid cancer, it is difficult to treat and usually is not curable.

Treatment requires surgery to remove nearly all of the thyroid and removal of surrounding lymph nodes.

By the time patients are diagnosed as many as 50% have cancer that has already spread to other organs such as lymph nodes. About 10% of patients have cancer that has already spread to the lungs or liver.