Bomb tests and thyroid cancer - screening program not recommended.

During the 1950s and 1960s, nearly 100 atmospheric nuclear bomb tests were conducted at a test site northwest of Las Vegas. One of the radioactive elements in the fallout from the tests was iodine-131, which concentrates in the thyroid gland when ingested or inhaled and has been linked to thyroid cancer. Approximately 160 million people living throughout the United States during the bomb tests might have been exposed to varying levels of iodine-131 for about two months following each test. Iodine-131 has a radioactive half-life of only about eight days, however, and the risk of harmful exposure decreased rapidly after each bomb test. Some people inhaled the radioactive iodine, but most were exposed indirectly by .consuming milk from cows or goats that grazed on contaminated pasture land.

Estimates of radiation exposure were based on factors such as people's age at the time of the tests, place of residence, and foods consumed (particularly milk). Evidence suggests that childhood exposure to radioactive iodine - especially before the age of 10 years - can increase the risk that a person will develop thyroid cancer at some point. Children who drank milk produced by cows or goats on family farms may have received higher-than-average exposure. This milk would have contained more iodine-131 than was present in commercially distributed milk, because it typically was consumed shortly after production, and the radioactive iodine had little time to decay. People who were teenagers or adults when the bomb tests were conducted, or who did not drink milk, are at very little risk of developing thyroid cancer from exposure to the fallout.

A report issued by committees of the Institute of Medicine (IOM) and the National Research Council (NRC) argues that the government should not sponsor national or regional thyroid cancer screening, despite the fact that exposure to radioactive iodine has increased the risk for some Americans. No evidence suggests that early detection of thyroid cancer through a routine screening program would prolong lives or lead to other health benefits. The kind of thyroid cancer linked to radiation exposure is rarely fatal. It can - and should be detected and treated promptly during routine medical care.

To screen for thyroid cancer, doctors first search for lumps on the thyroid either by feeling the throat or by performing an ultrasound test. Both methods detect nodules rather than cancer itself. Many adults have harmless, noncancerous lumps on the thyroid, so tissue samples of the nodules must then be taken. Approximately 25 percent of these samples are indeterminate or unsatisfactory, and some false positives occur. Furthermore, some small malignant nodules will not grow or cause health problems. If all or part of the thyroid is removed, however, a lifetime of hormone therapy is usually required.

A national or regional screening effort could therefore cause needless worry and unnecessary surgeries. Instead of undertaking such a program, the government should use resources to involve the public and the medical community in designing an information program about exposure to fallout, the risks of developing thyroid cancer, and potential benefits and drawbacks of testing for the disease.

Of people who are diagnosed with thyroid cancer linked to radiation, nine out of 10 live longer than 30 years after the cancer is found. Thyroid cancer in all forms accounts for less than one percent of total cancer deaths each year.