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Making Choices: Screening for Thyroid Disease

  • Posted: 08/01/2003

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Screening for Thyroid Disease

What is screening for thyroid disease?

Screening aims to detect thyroid disease early, before there are any symptoms.

  • Many people think screening is always a good thing. But there are good reasons why you might choose not to be screened for thyroid disease. Screening tests are never 100 percent accurate. Some people who are screened for thyroid disease will get an abnormal screening result even though they do not have thyroid disease. Others may receive a normal screening even though they have thyroid disease. These things happen with all screening tests.

  • Whether you think it is worthwhile to get screened is your decision. There is no right or wrong choice. Some people will choose to be screened. And others will choose not to be screened.

  • The information that follows will focus on the pros and cons of thyroid cancer screening. Screening for noncancerous thyroid disease that increases or decreases the amount of thyroid hormones in the body involves a simple blood test. It is unlikely to cause you any harm, other than the inconvenience and cost of the blood test. About 14 in 1,000 women and about 9 in 1,000 men aged 60 years or older probably have undetected thyroid disease involving abnormal thyroid hormone levels. Through screening, these people may be identified and treated. Treatment is likely to be effective for those with clearly abnormal thyroid hormone levels. There is no good evidence on whether treatment is helpful in people with only mildly abnormal thyroid hormone levels.

What is involved in thyroid cancer screening?

Cancer screening is not just a matter of having a quick test. You need to consider what might happen after you get your screening test result.

Options for thyroid cancer screening

Doctors screen for thyroid cancer by feeling the gland, to check for a lump or nodule. If a doctor feels a nodule, it does not mean cancer is present. Most thyroid nodules are not cancer.

There are two methods of investigating a thyroid lump or nodule: 1) ultrasound, to locate and describe the lump, and 2) biopsy, to determine if the lump may be cancerous. Thyroid ultrasound creates pictures by bouncing sound waves off the gland. This technique is painless and quick. But it cannot determine whether a lump is cancerous. The ultrasound device uses sound waves that people cannot hear. A computer uses the echoes to create a picture called a sonogram. From the picture, the doctor can see how many nodules are present, how big they are, and whether they are solid or filled with fluid.

If you choose to be screened by ultrasound, your doctor will arrange for you to have a scan at an x-ray practice or clinic. The scan is quick and painless. Thyroid nodules may be seen on the scan. If so, follow-up tests will generally be advised. These may be a repeat ultrasound scan in the future to see if the nodules have grown, fine needle aspiration, or surgery.

Confirmation of cancer requires biopsy, usually using a fine needle. Cells removed from the nodule during biopsy are directly examined in the laboratory.

What is fine needle aspiration?

A needle is put into the thyroid and cells are taken out. The cells are examined under a microscope. You may feel minor pain or get a bruise. A needle aspiration can usually tell whether there is cancer in the nodule. But in about 20 percent of cases the result is unhelpful, and people need to have another biopsy or surgery.

What are the pros of thyroid cancer screening?

#1 Reassurance for people who do NOT have cancer
Most people who are screened do not have cancer. These people benefit by being reassured that they do not have cancer.

#2 Early detection for people who DO have cancer
A few people will have cancer. These people will have their cancer found earlier than they would have otherwise, perhaps while it is very small. So, they may require less complicated treatment and have better chances of survival.

What are the cons of thyroid cancer screening?

#1 False alarms for people who do NOT have cancer
Some people will be falsely alarmed because a nodule is found. They may need to have repeat scans, fine needle aspiration, or surgery to see whether they have cancer. Ultimately, these people learn they do not have cancer. But they will have experienced stress and anxiety in the process of reaching a diagnosis, as well as inconvenience and possibly complications of unnecessary surgery.

#2 Uncertainty about the benefit of early treatment
Scientists know that most thyroid cancers can be cured. It is unclear if finding and treating those cancers early offers an added benefit. There are no reliable studies about the long-term benefit of thyroid cancer screening. No one knows for certain if thyroid cancers found early require less treatment than those found later.

#3 False reassurance for some people who DO have cancer
Screening does not find all the cancers. A few people will be falsely reassured. They do have cancer but their screening test is normal. So, they do not benefit from screening.

How many people have cancer correctly detected and how many people get false alarms?

The numbers of cancers detected and false alarms are different for screening by neck exam than for screening by ultrasound.

The charts that follow show the pros and cons of screening by neck exam and by ultrasound. The numbers on the charts are based on scientists' best guesses at how many people are affected. The exact numbers will vary for different places and people.

Screening 1,000 people by neck exam...

920-960 people will be correctly assured they do not have cancer.40-80 people will have false alarms and will be offered follow-up tests:
  • 40-80 people will be offered ultrasound scan
  • 20-40 people will be offered fine needle aspiration as well as ultrasound
  • 3-10 people will be offered surgery as well as ultrasound and fine needle aspiration
1-3 people will have cancer found early. They may need less complex treatment and may have better chances of cure.The 1-3 people who will have cancer found early may not have better chances of cure. They might just know for a longer time that they have cancer.

Screening 1,000 people by ultrasound...

800-850 people will be correctly assured they do not have cancer.150-200 people will have false alarms and will be offered follow-up tests:
  • 70-120 people will be offered repeat ultrasounds and 70-80 people will be offered fine needle aspiration
  • 10-15 people will be offered both surgery and fine needle aspiration
4-6 people will have cancer found early. They may need less complex treatment and may have better chances of cure.The 4-6 people who will have cancer found early may not have better chances of cure. They might just know for a longer time that they have cancer.

What is thyroid surgery?

Thyroid surgery may be needed to detect thyroid cancer that is not found by fine needle aspiration. Thyroid surgery is generally very successful. Most of the time only a part of the thyroid gland is removed. Nevertheless some people have adverse effects, which can include:

  • Damage to the parathyroid gland (next to the thyroid gland). This causes temporary low blood calcium and muscle cramps in 10 to 15 of every 1,000 people. A few people (about 7 of 1,000) will need to take calcium supplements permanently.
  • Needing to take thyroid pills. If the entire gland is removed, thyroid hormone replacement pills must be taken. If part of the gland is removed, between 1 and 10 people out of every 1,000 will need to take hormone replacement pills.
  • Damage to the vocal cords and having a hoarse voice afterwards. Generally this is temporary, but in about 7 of 1,000 people, the hoarseness is permanent.
  • Getting an infection in the wound and needing antibiotics (about 3 out of 1,000 people).
  • Bleeding during the operation and needing a blood transfusion (less than 1 of 1,000 people).
  • Dying from the anesthetic (less than 1 of 1,000 people).

*These are average rates and will vary with different people, places, and surgeries.

How can you decide whether to be screened for thyroid cancer?

Your options are:

  1. Continue with your usual health care. If you develop a symptom, see your doctor and have this symptom checked.

  2. Ask your doctor to screen you by neck exam.

  3. Ask your doctor to arrange an ultrasound.

Steps in making your decision. See below to work through these steps in decision-making:

Step 1: What is your estimated dose of I-131 from the Nevada tests?

Step 2: What is your likely risk of developing thyroid cancer?

Step 3: How important is each of the pros and cons of thyroid cancer screening to you?

Step 4: Which of the two methods of screening is best for you?

Step 5: What questions do you have before deciding?

Step 6: Discuss your decision-making with your doctor.