Thyroid for Dummies (19 page)

cell produces a hormone called
calcitonin
, which does not affect metabolism, but is involved in the regulation of calcium levels. This fact is useful because, after this cancer is treated by completely removing the thyroid, measurement of calcitonin levels at regular intervals is an easy way to diagnose a recurrence of this type of cancer. Medullary thyroid cancer is usually discovered when someone finds a lump. Other symptoms can include frequent loose stools and flushing of the skin.

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Medullary thyroid cancer differs from the others in that it has a tendency to run in families. One out of every four people with medullary thyroid cancer has inherited the condition, which is linked with certain genes. If you inherit those genes, then you are almost certain to develop medullary thyroid cancer at some time. In hereditary cases, either another member of the family will also have medullary thyroid cancer or the person will have the medullary thyroid cancer as part of a condition called
multiple endocrine neoplasia (MEN)
syndrome in which cancer can occur in other glands, too.

Two different types of MEN exist. Patients with MEN type II-A have a tumour in an adrenal gland (called a
phaeochromocytoma
) and the parathyroid glands in the neck. The part of the adrenal gland affected (the middle bit, called the
medulla
) makes a hormone called
epinephrine
(also called adrenaline), which mimics the effects of stress in the body – so these people get high blood pressure. They also get elevated levels of calcium as a result of the parathyroid tumour. MEN type II-B also includes the adrenal tumour that produces excessive amounts of epinephrine, but not the parathyroid tumour. The third feature of MEN II-B is a characteristic physical appearance with tumours in the mouth.

In 75 per cent of occurrences, medullary thyroid cancer is not hereditary and no other family member has it, but family history is closely checked, just in case.

Even in the absence of symptoms suggesting other endocrine tumours, all people diagnosed with a medullary thyroid hormone are screened to exclude tumours of the adrenal and parathyroid glands. If present, controlling these tumours with medication before surgery is important, as high blood pressure makes surgery on your neck extremely dangerous.

The important characteristics of medullary thyroid cancer include: ߜ It’s found in women more often than in men.

ߜ It’s not associated with exposure to radiation.

ߜ It’s more aggressive than papillary or follicular thyroid cancers, especially if it spreads to the lymph glands in the neck or to the bone and liver.

ߜ If one family member is diagnosed with medullary thyroid cancer, other family members should have their calcitonin levels checked. If a family member’s calcitonin is elevated, he or she should have the thyroid removed because cancer is almost always found or, if not yet present, will develop later.

ߜ Even when the calcitonin is not elevated in a family member, genetic testing can determine whether that person may eventually get a medullary thyroid cancer (see Chapter 14).

ߜ Measuring calcitonin levels reveals whether a tumour has spread or recurred after the removal of the thyroid.

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Some thyroid specialists advocate measuring calcitonin as a screening test for all nodules suspected to contain thyroid cancer. So far, this practise is not routine as the diagnosis is readily made with a fine needle aspiration biopsy.

After 10 years, about 50 per cent of people with medullary thyroid cancer who receive treatment are still alive.

Undifferentiated (anaplastic)

thyroid cancer

When thyroid cancer cells look so abnormal under a microscope that they do not resemble the thyroid cells from which they arose, the cells are described as
undifferentiated
. This type of cancer is very aggressive and rarely cured.

While 95 per cent or more of people with a differentiated thyroid tumour, such as a papillary or follicular thyroid cancer, are alive and doing well after ten years, less than 10 per cent of those with undifferentiated thyroid cancer survive more than three years. Fortunately, undifferentiated cancer is rare, accounting for only about 2 per cent of all thyroid cancers.

This cancer is aggressive and invasive. While lymph node invasion in the case of papillary cancer is not a bad sign, lymph node invasion due to an undifferentiated cancer predicts a bad outcome.

The cancer tends to attach to local structures like nearby neck muscles, the trachea, the oesophagus, and blood vessels, making surgery very difficult, if not impossible. The outlook is so bad that there’s little justification for extensive surgery that just causes mutilation without accomplishing a cure.

Important features of an undifferentiated cancer include: ߜ Males are affected twice as often as females.

ߜ It usually occurs in people over the age of 65.

ߜ It may occur in people with a distant history of radiation to the neck or face.

ߜ At the time it’s diagnosed, secondaries are often already found in local nodes and distant structures like the lungs, bone, brain, and liver.

ߜ Most people will die of this type of cancer within six months to a year of diagnosis.

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Staging Thyroid Cancer

For purposes of treatment, thyroid cancers are
staged
(divided into stages).

This means they are divided into those stages where the cancer remains within the thyroid gland, those where the cancer has spread, and those according to the characteristics of the tumour, such as its size. Knowing which stage a cancer is in is important, because a follicular cancer that has the same stage as a papillary cancer responds to treatment in the same way, while two follicular cancers at very different stages respond differently.

Thyroid cancer is divided into four stages: I, II, III, and IV (see Table 8-1). Which stage of thyroid cancer a person has is based on the TNM classification, which stands for Tumour, Nodes, and Metastases (the posh word for secondaries, distant sites to which the cancer has spread via the bloodstream).

Using this classification, doctors describe whether the tumour (T) is less than or equal to 1 cm in greatest dimension (T1), between 1–4 cm in size (T2), greater than 4 cm in dimension (T3), whether it extends beyond the thyroid boundary capsule (T4, whatever its size), or is non-assessable (TX) because testing is not possible for some reason.

For the nodes (N), N0 means no nodes are involved, N1 means regional nodes are involved, while NX means the nodes are non-assessable. Similarly, for spread to other sites, M0 means no distant metastases, M1 means distant metastases, while MX means the presence of distant metastases is not assessable.

Someone whose tumour is diagnosed early is likely to have a TNM classification of: T1, N0, M0, meaning their primary tumour is less than 1 cm in dimension with no nodes or distant metastases involved, which is the essential basis for diagnosing a thyroid cancer as Stage I. The final staging does also depend on your age, and whether or not you are under or over 45 years.

Table 8-1

Papillary and Follicular Thyroid Cancer Staging

Under 45 Years

45 Years and Older

Stage I

Any T, any N, M0

T1, N0, M0

Stage II

Any T, any N, M1

T2, N0, M0

T3, N0, M0

Stage III

T4, N0, M0

Any T, N1, M0

Stage IV

Any T, any N, M1

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So, for Stage I in someone under the age of 45 years, the key point for papillary and follicular cancers is that the tumour has not spread to distant sites, despite its size, and despite the involvement of local neck nodes. For someone over the age of 45 however, a Stage I cancer is only diagnosed if the tumour is less than 1 cm across (T1) and there are no nodes (N0) or metastases (M0). This diagnosis is made because age is an important factor in predicting the outcome of treatment in people with papillary and follicular thyroid cancers. If nodes are involved (N1) the cancer is always at least Stage III, whatever your age. If metastases are present, the cancer is always classed as Stage IV, whatever its size, node, or metastases status. Stage IV

thyroid cancers usually contain undifferentiated cancer cells.

To make classification even more complex, the TNM basis for staging a medullary tumour is slightly different than for papillary and follicular cancers, as age is not a factor that predicts outcome for this type of tumour (see Table 8-2).

Table 8-2

Medullary Cancer Staging

Stage I

T1, N0, M0

Stage II

T2, N0, M0

T3, N0, M0

T4, N0, M0

Stage III

Any Tl, N1, M0 (if nodes are involved, it’s always at least Stage III)
Stage IV

Any T, any N, M1 (if metastases are present, it’s always Stage IV) If this information is starting to look too complicated for you to digest, don’t worry – diagnosing the stage of your cancer is your doctor’s job. Ask your doctor to explain it to you properly if you wish to know more.

Treating Thyroid Cancer

These guidelines suggest that someone with a suspected thyroid cancer should be urgently referred to a specialist thyroid clinic and seen within two weeks. At the clinic, the patient sees a multidisciplinary team made up of professionals who are interested in, and expert at, treating thyroid cancers. This team normally includes an endocrinologist, a surgeon, an oncologist (cancer specialist) with support from a pathologist, medical physicist, biochemist, 13_031727 ch08.qxp 9/6/06 10:44 PM Page 98

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radiologist, and specialist nurse. The guidelines also point out the importance of giving patients full verbal and written information about their condition and treatment, with continuing access to guidance and support as well as lifelong follow-up.

The different types of thyroid cancer are treated in slightly different ways. If you have thyroid cancer your treatment usually starts as early as possible.

In fact, national guidelines insist that all decisions relating to your diagnosis and treatment are made within two weeks of your first consultation, wherever possible. They also state that you receive an appointment to see the clinical oncologist (cancer specialist) or nuclear medicine physician (who is an expert in radioactive iodine treatment) within two weeks of referral from a surgeon. And, that after your surgery, arrangements for radioactive iodine treatment (if needed) are made within several weeks. In theory, that means that treatment is not subjected to unnecessary delays, which is good news.

Papillary thyroid cancer

Most people with papillary cancer, especially those with tumours greater than 1 cm in diameter, node involvement (N1), or secondaries (M1), and those with familial disease or disease due to radioactive exposure, undergo surgery to remove their entire thyroid gland (a total thyroidectomy) and local lymph nodes. The surgeon takes care to leave intact the tissue next to the parathyroid glands and recurrent laryngeal nerve. This procedure helps to ensure that the parathyroid glands continue to function and the person’s speech is not damaged after surgery. If cancer is present in any lymph nodes, the surgeon removes as much non-essential tissue as possible, in what is known as a
modified radical neck dissection
.

In all cases, a total thyroidectomy is followed with radioactive iodine treatment to destroy any remaining thyroid tissue. After this, the person receives thyroxine hormone replacement at a dose that is high enough to suppress their natural production of thyroid stimulating hormone (TSH) from the pituitary gland (to less than 0.1 µU/ml (microunits per millilitre)). This dosage ensures that if a small remnant of thyroid tissue manages to survive both surgery and radioactive iodine treatment, TSH does not re-stimulate it into growth. Someone with a small papillary thyroid cancer of less than 1 cm in diameter and who has no nodes or metastases (T1, N0, M0) may undergo surgery to remove just the thyroid lobe in which the cancer is situated, plus the middle bit of the thyroid (isthmus). This operation is called a
lobectomy
and leaves part of the thyroid intact as the chance that cancer has spread into the other lobe is small. In this case, radioactive iodine is not given, and surgery is usually followed with thyroxine therapy to keep the TSH level suppressed.

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Distant metastases develop in 5–20 per cent of patients with differentiated (papillary and follicular) thyroid cancers, mainly in the lungs and bones.

Where they are accessible, surgical removal followed with radioactive iodine is the treatment of choice.

For secondaries in the bones, a combination of radioactive iodine, external beam radiotherapy, and orthopaedic surgery is used. For tumours that do not concentrate radioactive iodine, your management team will discuss other treatment options with you, such as
external beam radiotherapy
(in which the tumour is irradiated) and
chemotherapy
(using drugs that target rapidly dividing cancer cells) – both these approaches are designed to kill cancer cells so the tumour shrinks.

Follicular thyroid cancer

For follicular cancer, lobectomy is performed where the tumour is confined to the thyroid gland. If examination of the tumour under a microscope shows it’s a type of follicular tumour known as a
follicular adenoma
, then no further treatment is needed. If the tumour is classed as a follicular cancer, however, and it is under 1 cm in diameter with no signs of invasion (T1, N0, M0), lobectomy is followed with thyroxine hormone replacement to suppress production of TSH.