The diagnosis of cancer is terrifying for most patients because it has become
associated in our minds with pain and death. But, in fact, the outlook for
patients with thyroid cancer is usually excellent because:
Most thyroid cancer is easily curable with surgery
It causes little pain or disability
Novel and effective means of diagnosis and therapy are available for
several kinds of thyroid cancer.
Thyroid cancer usually presents itself as a lump or nodule in the thyroid
gland. However, it should be emphasized that most thyroid nodules (98% or
more) are benign. Unfortunately, it may be difficult to distinguish a benign
from a malignant nodule on the basis of symptoms and physical examination, even
with the help of laboratory tests including blood hormone levels and scans
(images) of the thyroid gland. Experienced hands and biopsy of thyroid nodules
usually provides the most valuable information in helping a physician to decide
whether a surgical intervention is necessary.
Who is at Risk for Thyroid Cancer?
Although we do not know exactly what causes thyroid cancers, cancers
are more likely to develop in patients who have received x-ray treatments in childhood
for enlarged tonsils, enlarged thymus glands, acne –all these practices have
been stopped several decades ago- and occasionally for other malignancies such
as Hodgkin's disease.
Routine diagnostic x-rays (like chest x-rays, dental x-rays, or thyroid
scans) do not cause such thyroid cancer.
Papillary Thyroid Cancer
A papilla is a nipple-like projection. Papillary cancers have multiple
projections giving them a fern or frond-like appearance under the microscope.
Tiny areas of papillary cancer can be found in up to 10% of
"normal" thyroid glands, when thyroid tissue is carefully examined
with a microscope. The more carefully a pathologist looks for these tiny
cancers, the more commonly they are found. These microscopic cancers seem to
have no clinical importance and are more a curiosity than a disease. In
other words, there does not seem to be a tendency for these small cancer-like
growths to enlarge and become more serious malignant tumors.
On the other hand, when papillary cancer grows enough to form a palpable
lump in the thyroid gland, we consider it clinically important, for it is
likely to continue to enlarge and may spread elsewhere in the body. Papillary
tumors make up about 70% to 80% of all thyroid cancers, and can occur at any
age. There are only about 12,000 new cases of papillary cancer in the United
States each year, but because these patients have such a long life expectancy,
we estimate that one in a thousand people have or have had this form of cancer.
Papillary cancer tends to grow slowly and to spread by means of the lymphatic
system to lymph glands in the neck. About one third of the patients
who undergo surgery for papillary cancer, the tumor has already spread to
surrounding lymph glands (lymph node metastasis). Fortunately, the generally
excellent outlook is usually not altered by lymph gland metastases.
The papillary cancer may also spread from one side of the thyroid to the
other through the lymphatic system, again without affecting the patient's
85% of patients with papillary carcinoma have a primary tumor that is
intrathyroidal (confined to the thyroid gland itself). The 25-year mortality
rate from cancer in this situation is about 1%. This means that only 1 out of
every 100 such patients have died of thyroid cancer by 25 years later. By that
time the vast majority of them have been permanently cured. The prognosis is not
quite as good in patients over the age of 50, or in patients with tumors larger
than 4 centimeters (1 1/2 inches) in diameter.
Since the outlook in patients with intrathyroidal primary tumors is so
favorable, it is important that therapy not be hazardous. Radical surgery is
almost never indicated for this mild type of papillary cancer. Although up to
10% of patients with intrathyroidal papillary cancer will have a recurrence of
tumor, recurrences are generally due to the growth of tumor cells within lymph
glands in the neck and are not life threatening. They are usually removed
The prognosis is not as good in patients where the cancer has grown through
the thyroid into surrounding tissues. Specifically, this means spread through
the fibrous capsule that surrounds the thyroid gland into the tissues of the
neck, and not the lymph node involvement discussed above. In a very small
percentage of patients (about 5%), the cancer eventually spreads through the
blood stream to distant sites, particularly the lungs and bones. These distant
tumor sites (metastases) can often be treated successfully with radioactive
iodine (see below). Although young patients who have papillary thyroid cancer
generally have an excellent outlook, patients under the age of 20 have a
somewhat higher risk of spread to lungs.
Follicular Thyroid Cancer
The normal thyroid gland is made up of sphere-shaped structures called
follicles. When a thyroid cancer contains these normal structures, the cancer is
called a follicular cancer. Follicular cancer makes up about 10-15% of all
thyroid cancers in the United States, and tends to occur in somewhat older
patients than papillary carcinoma.
Follicular cancer of the thyroid is considered to be more aggressive than
papillary cancer. In about one-third of patients with follicular thyroid cancer,
the tumor is minimally invasive and tends not to spread. The prognosis is
excellent in this situation. In the other two-thirds of patients, the follicular
cancer is more invasive. It may grow into blood vessels and from there spread to
distant areas, particularly the lung and bones. In general, the prognosis is
better in younger patients than in those over 50 years of age.
Treatment of Thyroid Cancer
The primary therapy for all forms of clinically relevant thyroid cancer is
surgery. For more aggressive papillary and follicular cancers, the generally
accepted approach is to remove the entire thyroid gland, or as much of it as can
be safely removed. For intrathyroidal papillary cancer and minimally invasive
follicular thyroid cancer, surgeons and endocrinologists continue to debate the
merits of total thyroid removal versus the removal of just one lobe and the
tissue connecting the two thyroid lobes, known as the isthmus.
Since the outlook is so good for intrathyroidal papillary cancer and
minimally invasive follicular cancer, independent of the extent of surgery, it
has been difficult to prove which of the two surgical approaches is preferable.
Therefore there are no absolute rules for the management of these cancers.
Although the general characteristics of tumor behavior are understood, in any
particular patient the choice of treatment is best made by physicians skilled in
the management of patients with thyroid cancer.
The thyroid gland normally concentrates iodine from the bloodstream at
concentrations reaching 1000 times higher than other tissues. This property off
thyroid tissue has been exploited for treatment. Large doses of radiation using
radioactive isotopes of iodine can be directed to the cancer, without damage to
To undergo radioactive iodine therapy for thyroid cancer that has spread the
entire thyroid gland must almost completely be surgically removed. Once that has
been done, patients with a residual tumor in the neck or known distant
metastases can then undergo a scan with a test amount of radioactive iodine
(usually about 2 to 10 millicuries –a measurement of radioactivity). If a
significant amount of iodine is concentrated in the areas of thyroid cancer, a
larger therapeutic dose of radioactive iodine (usually 150-200 millicuries) can
be administered in an attempt to destroy the tumor.
A patient who receives treatment with large doses of radioactive iodine must
stay several days in the hospital, until the amount of radioactivity in the body
falls to levels which will not be hazardous to other people. However, this
treatment has proved to be safe and well-tolerated, and has even been able to
cure cases of well-differentiated thyroid cancer after the tumor has spread to
Because of the safety and effectiveness of radioactive iodine in patients
with more aggressive thyroid cancer, many physicians also use it routinely in
patients with less aggressive papillary and follicular cancers. In this
situation, radioactive iodine is used to destroy tiny remnants of thyroid tissue
still present after surgery. This may improve the outlook and makes it easier to
monitor patients for tumor recurrence using a blood test for thyroglobulin (see
If well-differentiated thyroid cancer continues to spread, even after surgery
and the administration of radioactive iodine, then external radiation therapy
may be helpful. Chemotherapy is usually not very effective in this situation.
How are Thyroid Cancer
Periodic follow-up examinations are essential for patients who have had
surgery for papillary or follicular thyroid cancer, because recurrences
sometimes occur many years after apparently successful surgery. These follow-up
visits should include a careful history and physical examination, with
particular attention to the neck area.
Radioactive iodine scanning to obtain images of the neck and whole body may also
It is also helpful from time to time after surgery to measure the blood level
of thyroglobulin. This substance is released by normal thyroid tissue and also
by well-differentiated thyroid cancer cells. The blood level of thyroglobulin is
very low after total thyroid gland removal, and in most patients who are taking
thyroid hormone after thyroid surgery. An elevated or rising level of
thyroglobulin generally implies persistent or growing thyroid cancer, but does
not necessarily imply a poor prognosis. A high thyroglobulin level found in a
follow-up examination alerts the physician to the possibility that other tests
may be needed to be sure the tumor is not recurring. Unfortunately, in some
thyroid cancer patients the presence of interfering antibodies in the blood may
prevent accurate thyroglobulin measurement.
What about Thyroid Hormone
Even if part of the thyroid remains, therapy with levothyroxine (e.g. Synthroid,
Levothroid) not only is necessary to mantaining normal health, but is an important part of the follow-up care in thyroid cancer
patients, since studies have shown that cancer is more likely to recur in those
patients who do not take this medication. The thyroid hormone should be
administered in sufficient quantities to suppress TSH levels.
New, sensitive TSH measurements are extremely useful for monitoring TSH
concentrations and confirming that the serum TSH is just below normal in
patients at low risk of cancer recurrence. Patients with more aggressive forms
of papillary or follicular cancer probably should take larger doses of thyroxine
in order to suppress TSH to just below normal levels.