About 23,600 people are diagnosed with thyroid cancer (search) each year in the United States, according to the American Cancer Society (search). There are several types and it was not immediately known which type Chief Justice William H. Rehnquist (search) has.

Some types of thyroid cancer "can be highly effectively treated with surgery, iodine, and thyroid suppressant medications," and the patients can live long, healthy and normal lives, said Dr. Paul Wallner of the National Cancer Institute (search).

Other types are more aggressive and the patients don't do as well.

Two key factors that determine outcome are what type of tumor the patient has and what type of surgery was done, Wallner said.

The patient's age, ability to tolerate surgery and any possible complications also play large roles. Rehnquist is 80.

Supreme Court officials said that a tracheotomy (search) was performed on the chief justice.

That procedure, which involves opening the throat and inserting a tube, might be done for two reasons: "Simply in anticipation of routine thyroid surgery or ... because he was having breathing difficulty," Wallner said.

The cancer society estimates 1,460 Americans will die of the disease this year, with slightly more deaths among women than men.

Of the estimated new cases, 17,640 are expected to be in women and 5,690 in men, the group says.

The thyroid gland, located in the neck, produces hormones that help regulate the body's use of energy.

Overall, Wallner said thyroid cancer is one of the less frequent malignancies. He said it tends to occur in young adults, then decline and then increase again in frequency in older persons.

The thyroid is located below the Adam's apple in the throat. It has a lobe on each side of the throat joined by a narrow connection.

The major types of thyroid cancer are:

Papillary cancer (search), which makes up most thyroid cancers, 60 percent to 70 percent. It is more common in women than men and in younger people, but when it occurs in older people it can spread rapidly. It often strikes people who received radiation therapy for throat problems as youngsters.

Follicular cancer (search), which causes about 15 percent of all thyroid cancers. This is more common in older people.

Anaplastic cancer (search), the most aggressive type of thyroid cancer, makes up about 5 percent of thyroid cancers. It grows very quickly, usually with a large growth in the neck, and tends to spread throughout the body.

Medullary cancer (search), which begins in the gland and tend to spread through the lymphatic system.