Thyroid Nodules and Thyroid Cancer

The Thyroid Nodule
The thyroid nodules are "lumps" occurring in or on the thyroid gland. They are fairly common and can be found in about 3% of women and 1% of men. Most nodules are benign but some are malignant. Because of the risk of thyroid cancer and the high cure rate after surgery, most nodules were removed until about 10 years ago. Pathologic examination after surgery revealed less than 10% of these nodules were malignant leaving over 90% that could have been left alone or treated medically. Because it is usually impossible to tell if a nodule is benign or malignant on a routine physical examination, we rely heavily on tests to help in deciding which nodules can be treated medically and which nodules really need surgery. This has reduced the need for "unnecessary surgery" considerably in the past ten years.
Some features from the history and physical examination are helpful statistically. For example, while nodules are more frequent in women, a nodule in a man is more likely to be cancer. Also nodules in younger patients are more likely to be malignant. The presence of lymph node enlargement in the neck and hoarseness increases the risk of cancer. Paradoxically, a single nodule is more likely to be cancer than a thyroid gland that has multiple nodules. Almost all nodules (benign or malignant) are painless and seldom cause symptoms or weight loss. A history of rapid growth in a nodule is especially worrisome.
While thyroid cancer is only about the 20th most common cancer; in the fifteen to thirty-five year old age group, it is the second or third most common cancer. A rare type of thyroid cancer produces an abnormal hormone, calcitonin, that can be measured in the blood but there is no blood test for the vast majority of thyroid cancers. Blood tests are usually done to look for other types of thyroid nodules such as thyroiditis, mild degrees of hyperthyroidism or hypothyroidism. If such tests are abnormal, it may give indirect evidence against malignancy.
As stated earlier in Chapter III, during the 1940's and 1950's it was common to treat children and teenagers with radiation for benign disease. Even newborn infants were sometimes given radiation for an enlarged thymus gland which was thought to cause airway obstruction. Older children received "x-ray treatment" for enlarged tonsils and adenoids, to remove birth marks, and to treat ringworm of the scalp. Teenagers received the radiation for acne. Unfortunately, this began causing thyroid problems 15-30 years later and approximately one-third of patients have developed some type of goiter. The incidence of thyroid cancer in people who received this radiation is 7%.
Therefore, a rapidly enlarging nodule in a thirty year old man who has a history of radiation treatment in childhood raises a high degree of suspicion of thyroid cancer. However, such a history only statistically raises the chances of malignancy, since the incidence in any individual is either 0% or 100%. Therefore, we still check each individual carefully before recommending surgery.
For the past twenty years the thyroid scan has been the most useful test in patients with thyroid nodules. Nodules that concentrate iodine greater than normal thyroid tissue (hot nodules) are never cancerous. Unfortunately, only about 15% of nodules are "hot". The remaining 85% of nodules may be cancer but the majority of these nodules will also be benign. Frequently, the scan uncovers other small nodules that are not felt on physical examination. As stated earlier, this decreases the likelihood of cancer. This "hot" or "cold" classification only holds for scans done with iodine, not with scans done using technetium.
Camera thyroid scan of a "hot" nodule
Ultrasound is used on cold nodules to differentiate cysts from solid nodules. Since cysts are usually (but not always!) benign they can be drained with a needle and followed without surgery.
Camera thyroid scan of a "cold" nodule
Thyroid Needle Biopsy
The most accurate method of determining if a nodule is benign or malignant is to examine the thyroid tissue under a microscope. Until recently, the only method of obtaining a tissue diagnosis was a surgical biopsy. This is highly reliable, but involves hospitalization, discomfort, major expense, and several risks such as bleeding, infection, and scarring. Needle biopsy avoids these problems and risks and is almost as accurate as a surgical biopsy.
The routine use of needle biopsy of thyroid nodules began in the 1980's after doctors at the Henry Ford Hospital in Detroit and several other centers showed that one could differentiate cancer from benign nodules using this technique with much more accuracy than scans or blood tests. The procedure is carried out in the office with minimal discomfort. Very small needles are used (much smaller than the needles used to draw blood from the arm). Except for bruising, no complications have occurred and the procedure takes approximately 20 minutes. At least six different specimens are taken and the slides are prepared and sent to a pathologist, a doctor who is trained to interpret the cells. About five percent of the time it is impossible to obtain enough tissue for diagnosis. Another 20% are inconclusive. This is because some thyroid cancers closely resemble normal thyroid tissue. The other 75% of biopsies are read as either evidence of cancer or evidence of a benign nodule. Accuracy is better than 90%; however benign nodules must be watched and followed closely to be sure that they behave as benign nodules (i.e. don't grow after starting treatment). About 15% of biopsies are read as malignant and 60% are read as benign. A diagnosis of cancer indicates to the surgeon that he should go ahead with removal of most of the thyroid gland rather than the old method of removing just the nodule or one side of the thyroid and then having to go back to a second operation if cancer were found.
If a nodule is found to be benign on needle biopsy, a person is then put on thyroid hormone, one tablet a day, to suppress the thyroid (keep it inactive). The nodule should no longer grow and many atrophy (become smaller) over the next one to two years. The size of the nodule is monitored at three or four month intervals. If any enlargement occurs or the nodule does not decrease in size after two years, a repeat needle biopsy can be done. When the nodule decreases, the person should continue on thyroid hormone indefinitely or the nodule will recur. In this respect the person is no different than the one who had surgery. Both should remain on thyroid hormone forever!
Types of Thyroid Cancer
Papillary and Follicular
Although there are several types of thyroid cancer the vast majority are papillary, follicular, or a mixture of these two types of cancer. This cancer is extremely slow growing compared with most other cancers; therefore, it offers a very excellent chance of cure. So good was the "cure rate" that for many years it was not felt necessary to follow patients after their surgery: "The patient with thyroid cancer will generally outlive his surgeon". However this was partially true because the average age of the thyroid cancer patient is twenty years less than the average age of a surgeon. If a patient is found to have thyroid cancer today, then he is followed forever!
Unlike most other cancers, thyroid cancer seldom recurs during the first five years. In a study of almost 600 thyroid cancer patients done in 1977, it was found that after twenty years, patients who had only half their thyroid gland removed were five times more likely to have a recurrence of their disease than those in whom a total or near total thyroidectomy was done. It was shown that patients who had both sides of their thyroid gland removed, followed by a dose of radioactive iodine, and who took thyroid medication had a recurrence rate of less than 5% after twenty years. Today this is a standard treatment for thyroid cancer.
At surgery it is necessary to remove at least 90% of the thyroid gland (total, near total, or subtotal thyroidectomy). If only half of the thyroid was removed, a second operation is necessary to remove most of the opposite side. An exception to this rule is the very small (1.5 cm or less) cancer with no evidence of metastasis.
No thyroid replacement is given after surgery and the patient is allowed to become hypothyroid which usually takes 3-6 weeks as indicated by a rise in the TSH. A scan of the neck will show if thyroid tissue is still present and a dose of radioactive iodine is given to "ablate" this tissue. The patient is then put on thyroid replacement taking at least 1 microgram of L-thyroxine per pound of patient weight. TSH is then checked. If the TSH is less than 0.5, the patient remains on this dose of thyroid replacement indefinitely.
A follow-up scan is done at the end of the first year. This follow-up scan is done while the patient is off thyroid replacement. Because L-thyroxine has a half life of 6.7 days, it requires approximately six weeks for this medication to completely "clear" the body. The patient is put on Cytomel (which has a half life of 48 hours) six weeks prior to his scan. Then Cytomel is stopped after four weeks. This means that the patient is only off his thyroid replacement for approximately two weeks before his scan. If any remaining thyroid cancer is detected on a follow-up scan, it is treated with surgery or radioactive iodine 131.
Recently, a blood test which indicates a recurrence of thyroid cancer in patients has been developed. This test is simple and has the advantage of not having to stop a patient's thyroid medication prior to performing it, as in the case with thyroid scan.
Thyroid tissue (both normal tissue and cancerous tissue) produces a protein called thyroglobulin which is measured by performing a blood test. Patients with thyroid cancer have about the same amount of thyroglobulin as normal people; however, after removal of all the thyroid gland by surgery and radioactive iodine ablation, the thyroglobulin level falls to near zero. By monitoring the thyroglobulin (TG) level on these patients with a yearly blood test, a recurrence of the thyroid cancer can be detected if the patient's blood shows a rise in the thyroglobulin level. In the past thyroid scans were performed at periodic intervals of one to five years in order to check for recurrent cancer. This necessitated stopping thyroid hormone. Now scans are not done after the first year unless the thyroglobulin level rises or another lump occurs in the neck.
Other types of Thyroid Cancer
A rare type of thyroid cancer (medullary cancer) produces a hormone called calcitonin. Medullary cancer is more malignant than papillary or follicular cancer just described. When elevated levels of calcitonin are found in the blood, it is indicative of medullary cancer. Calcitonin disappears from the blood after the cancer is removed, and its level should be periodically checked to detect early recurrence. Many of the cases are hereditary, and these patients have a unique genetic mutation in the RET proto-oncogene. This mutated gene can be detected from birth, many years before the cancer occurs. Therefore, relatives of patients having medullary cancer must be checked for this mutation in the RET proto-oncogene to see if they will develop this type of cancer. This will allow the cancer to be "cured" before it develops.
A fourth type of thyroid cancer called anaplastic cancer is very malignant, but it is less common than the other types and occurs primarily in elderly people.
Occasionally, other types of cancer will involve the thyroid gland such as lymphoma or metastatic cancer from another organ (i.e. kidney). The treatment depends upon the type of primary cancer. Needle biopsy is usually able to differentiate the type of cancer involved and allows the surgeon to plan his surgery appropriately before the operation.
Thyroid Surgery
Thyroid surgery is presently done today for proven or suspected thyroid cancer. Although it may occasionally be used for other types of goiter, medical treatment is generally better for non cancerous disease. The "old days" of removing all goiters or thyroid nodules are gone. Surgery of the neck remains a formidable operation. The complication rate among the best surgeons is approximately 4%. The major complications are:
Vocal Cord Paralysis
Change in voice. This occurs when there is damage to one of the nerves that controls the vocal cords.
Hypoparathyroidism due to Parathyroid Gland Damage
Most people have four small parathyroid glands that control their calcium balance. As long as there is one good functioning parathyroid gland, no problem occurs. However, these small glands are very susceptible to damage during thyroid surgery. The damage may be temporary or permanent. If damaged, the calcium level drops and can cause muscle contractions and seizures shortly after surgery. Correction requires giving calcium IV and orally. If the damage is permanent, the patient will end up taking Vitamin D and calcium the rest of his life and calcium levels will need to be checked frequently.
Since virtually all patients who undergo thyroid surgery will take thyroid hormones afterwards, hypothyroidism does not occur after surgery unless the patient stops taking his thyroid medication.
Scar formation is variable with some patients forming a scar that is hardly noticeable and other forming unsightly scars. Surgeons make the incision in the skin line in the hopes that the scar will be less noticeable. Children sometimes form more noticeable scars because keloid formation seems more common in children. When thyroid surgery must be repeated, the risk of complications is much higher than on the initial operation. This is because the anatomy is different when the second operation is done and scar tissue has formed in the neck. The likelihood of damage to a nerve or parathyroid gland is much higher.
When all goes well, thyroid surgery is well tolerated and recovery is rapid. Most patients are back to full activity within two weeks. Unfortunately, "complications" are largely unavoidable due in part to the variable anatomy of the neck. Every effort should be made to avoid surgery unless it is necessary; however, surgery should not be delayed once the diagnosis of probable cancer is made.
Merck Serono Website
Merck Website