Cancer of the thyroid, a butterfly-shaped gland in the neck that secretes hormones, is on the rise in this country, and is expected to strike 23,600 Americans this year and kill 1,460, said Dr. Michael Thun who heads epidemiological research for the American Cancer Society in Atlanta. Most of the increase is due to better detection, because of CT or ultrasound imaging that can find small tumors that would have been missed in the past.

In its most common forms, the survival rate with thyroid cancer is 85 percent at 40 to 50 years, said Dr. Marshall Posner, medical director of the head and neck oncology program at Dana-Farber Cancer Institute.

Anaplastic thyroid cancer, the type Rehnquist is believed to have, is rare, but far more deadly, typically killing victims in three to six months.

As for Chernobyl, despite some data studies suggesting a possible link, that appears unlikely. In the 1986 accident in Ukraine, large quantities of radioactive iodine were spewed from the nuclear reactor onto the ground, where cows ate contaminated grass and produced contaminated milk, said Elaine Ron, a senior investigator in the radiation epidemiology branch of the National Cancer Institute. Radioactive iodine is taken up by the thyroid gland, where it can cause cancer. Researchers have documented a sharp increase in thyroid cancer in people who were under 18 and lived near Chernobyl at the time of the accident.

In the US, radioactive fallout occurred in parts of the West after nuclear weapons testing in the 1950s, but there has been no proven link to an increased risk of thyroid cancer, according to the National Cancer Institute. There is a link, however, between receiving radiation to the head and neck as a child and subsequent thyroid cancer.