Cancers of the Thyroid
There are four distinct types of thyroid cancer:
- Papillary carcinoma- this develops from follicular cells and
grows quite slowly. It is usually found in only one lobe (side)
of the gland
- Follicular carcinoma- this develops from follicular cells,
too,but is less common than papillary. It also grows slowly.
(Papillary and follicular cancers make up nearly 90% of all
thyroid cancers.)
- Medullary carcinoma- this develops in C cells, often as part
of a syndrome called "multiple endocrine neoplasia."
- Anaplastic carcinoma- this is a rare, poorly differentiated
and fast-growing tumor that develops from other, better differentiated
tumors. The speed of its growth makes it difficult to treat.
Risks factors for thyroid cancer include:
- Family history- goiters in the family increase risk for papillary
cancer; medullary cancer in the family increases the medullary
cancer risk
- Radiation exposure- Pre-1950 low-dose radiation treatments
for acne or tonsillitis; radiation treatments for Hodgkin or
non-Hodgkin lymphoma in the head an neck
- Diet low in iodine
- Gender- women get more thyroid cancer than men
- Ethnicity- Caucasians get more thyroid cancer than blacks
Symptoms are varied, and may include:
- A lump in the front of the neck
- Hoarseness
- Trouble swallowing
- Pain in the throat or neck
- Swollen glands in the neck
- Persistent cough
The diagnostic process begins with a thorough physical exam.
Palpation of the neck for any anatomical distortions or masses
is particularly important. The doctor will also check some blood
tests to measure the level of thyroid hormone and of "thyroid
stimulating hormone" (from the pituitary). He may also check
calcitonin levels. Ultrasound tests help to distinguish between
hollow "cysts" in the gland and solid tumors, while
radionuclide scanning will separate functioning ("hot")
nodules from non-functioning, "cold" nodules (the latter
more likely to be cancerous).
Often, the head an neck surgeon can obtain some cells from a
thyroid mass by using a "fine needle aspiration" right
in the office. After numbing the area with local anesthetic, he
can insert of tiny needle into several parts of the mass to sample
cells for the cytologic pathologist. When this sort of test is
inconclusive, the surgeon may recommend open biopsy or removal
of the nodule-containing lobe under general anesthesia.
Staging
TNM is an abbreviation for tumor (T), node (N), and metastasis
(M). Doctors look at these three factors to determine the stage
of cancer.
T0: There is no evidence of a tumor.
T1: The tumor is 1 cm or less and limited to the thyroid.
T2: The tumor is at least 1 cm, but not more than 4 cm, and is
limited to the thyroid.
T3: The tumor is larger than 4 cm, but does not extend beyond
the thyroid.
T4: The tumor is any size and has extended beyond the thyroid.
The "N" in the TNM system stands for lymph nodes, the
small, bean-shaped organs that help fight infection.
N0: There is no evidence of cancer in the lymph nodes.
N1a: Cancer has spread to lymph nodes in the neck on the same
side as the tumor.
N1b: Cancer has spread to lymph nodes on both sides of the neck,
the opposite side, the middle of the neck or the chest (mediastinal).
The "M" in the TNM system describes cancer that has
spread to other parts of the body.
MX: distant metastasis cannot be evaluated.
M0: cancer has not spread to other parts of the body.
M1: cancer has spread to other parts of the body.
Stages using TNM
(Papillary or follicular tumors in those under age 45)
Stage I: a tumor (T) with no spread to lymph nodes (N0) and no
distant metastasis (M0).
Stage II: a tumor (T) with any metastasis (M1) regardless of
whether it has spread to the lymph nodes (N).
Stage III: any invasive tumor (T4) with no spread to lymph nodes
(N0) or metastasis (M0), or any tumor (T) that has spread to the
lymph nodes (N1).
Stage IV: This stage describes all tumors when there is metastasis
(M1).
(Papillary or follicular tumors in those over age 45)
Stage I: a tumor (T) with no spread to lymph nodes (N0) and no
distant metastasis (M0).
Stage II: any larger, noninvasive tumor (T2, T3) with no spread
to lymph nodes (N0) and no metastasis (M0).
Stage III: any invasive tumor (T4) with no spread to lymph nodes
(N0) or metastasis (M0), or any tumor (T) that has spread to the
lymph nodes (N1).
Stage IV: This stage describes all tumors when there is metastasis
(M1).
(Medullary carcinomas)
Stage I: a small tumor (T1) with no spread to lymph nodes (N0)
and no distant metastasis (M0).
Stage II: any tumor (T) with no spread to lymph nodes (N0) and
no metastasis (M0).
Stage III: any tumor (T) that has spread to lymph nodes (N1),
but has not metastasized (M0).
Stage IV: evidence of metastasis (M1). All undifferentiated
anaplastic thyroid tumors are stage IV
Treatment
A number of modalities have place in the treatment of thyroid
cancers. Surgery, hormonal treatments, radioactive iodine therapy,radiation
and chemotherapy are all used, depending upon the size and location
of the tumor and the patient's general health.
Surgery is the main treatment in most cases.
Depending upon the tumor type and size, the head and neck surgeon
may remove the lobe containing the nodule ("lobectomy"),
or the entire thyroid ("total thyroidectomy"). If there
is reason to suspect lymph node involvement, the surgeon will
also perform a "neck dissection" to remove the nodes.
When the entire gland is removed, the body will no longer produce
thyroid hormone. Therefore, doctors will place the patient on
hormone replacement with a pill.
Four tiny glands called "parathyroid" are located on
the back of the thyroid. They are very important to calcium metabolism.
Although the surgeon will try to leave at least one gland in place
when performing thyroidectomy, this is not always possible. If
they are all lost or function poorly, the patient will be placed
on calcium supplements and vitamin D after surgery.
Because the thyroid gland soaks up virtually all of the body's
iodine, radioactive iodine is quickly concentrated
in any thyroid tissues after administration by doctors. The radiation
produced by this helps to destroy any cancerous thyroid cells
not removed by surgery. Radioactive iodine is used for many with
papillary and follicular cancers, but not for the other tissue
types. If the cancer has spread beyond the surgical site, pain
and swelling may occur wherever the metastatic cells are located.
Because the salivary glands also concentrate iodine, patients
may experience swelling of these glands and dry mouth for a time.
Those treated surgically for papillary, follicular and medullary
cancers will require thyroid hormone therapy after surgery. This
serves a dual purpose: it replaces the hormone that they can no
longer produce, and it slows the growth of any cancer cells that
may remain. This latter effect only relates to differentiated
cancers.
External radiation therapy uses high-energy
x-rays to kill cells. The treatment is usually given five days
a week for about five to six weeks either in a hospital or outpatient
facility. Radiation therapy is used only for patients with advanced
thyroid cancer that has not responded to radioiodine therapy.
Radiation therapy may be given after completion of surgery.
Although chemotherapy has a role in the treatment
of some thyroid cancers, its use is determined on an individual
basis and is most often administered as part of a clinical trial
(research study).
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