Thyroid
Cancer
Introduction: Thyroid
cancer is the most common among the cancers of the endocrine glands. It is more
common among women than men. The incidence of thyroid cancer among women is about
6 per 100,000 whereas men have an incidence of about 2.5 per 100,000. In 1995
in the US there were 13,900 new cases of thyroid cancer and 1,120 died from it
(Ref.1, p.1629). Although we speak of thyroid cancer as if it were one
type of cancer, it is in reality a collection of very diverse cancers that are
classified by their histology, the appearance under the microscope. The reason
this is important to know is that the rate, at which the various types of thyroid
cancer grow, is vastly different. The faster the cancer grows, the more difficult
to control and the deadlier it is. I will explain this in more detail below. There
seems to also be a difference whether or not the thyroid cancer is found in a
younger or older person. The older the person, the more malignant the growth behavior
and the worse the prognosis.
Anatomy:
As this image shows
the thyroid gland is situated just below the larynx (voice box) and embraces the
trachea (windpipe). The two lobes on each side are connected via the slimmer isthmus,
which is the middle part in the front. Many thyroid cancers often start in one
of the lobes, but there is a higher risk to develop an identical cancer in the
other lobe later in life and this has become important for diagnosis and treatment.
Histopathology/Types
Of Thyroid Cancer There are 4 distinct types among thyroid
cancers, which are described in more detail under these links. It
is important for the cancer specialist to distinguish between the four separate
histological subtypes of thyroid cancer as the growth patterns are different.
Also, the responses to various therapeutic modalities is quite different depending
on what histological type is found in the patient. The biopsy is sent to the pathologist
and usually one of the following types of thyroid cancers is diagnosed.
Papillary
Thyroid Cancer This is the most common thyroid tumor found at the time
of surgical removal. About 75% are of this histological type, which is medically
also known as papillary thyroid adenocarcinoma. It is usually associated with
a less invasive, slower growth behavior, in other words persons affected with
such a tumor can almost experience a normal life expectancy. The majority
of this type (90%) are variants with a good prognosis. They are the micropapillary,
encapsulated, solid and follicular variants. The 5 year survival of this group
is 95%, the 10 year survival is 85%. However, an important other 10% of this group
is associated with a poor prognosis and they are the tall cell, the columnar cell
and the diffuse sclerosing types. It is these variants, which are often found
in the older population. They are more invasive and form metastases by invading
neighboring areas, which contain a lot of blood vessels. They metastasize into
the lungs and bone thus leading to premature death.
Follicular
Cancer This type of thyroid cancer has a worse survival than the papillary
thyroid cancer. About 15% of all cases have this appearance under the microscope.
The 5 Year survival with optimal treatment is 80%, the 10 year survival is 65%.
Medullary
Thyroid Cancer About 5% of all thyroid cancers are of this type. This
is a special type of tumor as it is a tumor of the C type cells of the thyroid,
which produces the hormone calcitonin. Often this type of tumor is associated
with a familial genetic type of thyroid cancer. The cure rate is usually good,
provided it is found early on in the disease and treated appropriately. 10 year
survival used to be 50%, but with early diagnosis and aggressive therapy can be
as good as 80 to 90%.
Anaplastic
Thyroid Cancer The remaining 5% of all thyroid cancers belong to this
immature cell type cancer. It is a very fast growing cancer, which spreads early
on to other organs. The survival rates are dismal with overall survival rates
of only 7 months to at the most 2 years from the beginning of the diagnosis. About
35% of these cancers develop out of a papillary thyroid cancer in the elderly,
which may be a clone of resistant cancer cells that eventually kill the patient.
Thyroid
Nodules And Cancer: The thyroid gland has a tendency to produce
nodules (lumps) in one or both lobes. In the US about 4 to 7 % of the population
have benign thyroid nodules. This is more common in women than in men. The frequency
of nodule development throughout life is very constant and is 0.08% per year.
For some reason thyroid cancer seems to develop in these nodules and it does so
with a frequency of 10 to 20% of these nodules. When there has been an exposure
to radiation (x-rays, atomic energy from the Hiroshima bomb, nuclear accident
disaster) this rate can go up to 30 or 40% of cancer in thyroid nodules.
Summary:
As in other cancers early detection and surgical excision is of the utmost
importance. The thyroid gland is easily palpable right under the voice box and
even a small nodule can be picked up by the patient. The key for the patient is
to take action after the detection of a thyroid lump as described above. A biopsy
is done to show what cell type there is. If it is cancer, then it must be removed.
Following removal there must be a proper follow-up at regular intervals to make
sure that the cancer does not come back. |
