About Thyroid Cancer

Author : Bhadresh Bundela

Thyroid cancer
Thyroid cancer is classified firstly into differentiated types or undifferentiated (also called anaplastic) carcinomas, secondly there is group of medullary carcinomas and lastly there are the lymphomas. Differentiated carcinoma is so-called because the cancer looks (down the microscope) like the thyroid gland tissue from which it has derived.
There are two types: the commoner papillary type (60% of all thyroid cancer) and the follicular type (17% of the total). The importance of distinguishing the diffentiated histology is that these are the types of thyroid cancer which retain the ability to concentrate iodine. If the iodine is made into a radioactive iodine isotope, then this radio-iodine is a tumour specific lethal weapon. It is the differentiated types of thyroid cancer that form the majority of cancers of this gland and correct management is attended by high cure rates.
Anaplastic or undifferentiated carcinomas of the thyroid retain little of the features of the original thyroid gland as discerned down the microscope. They tend to be faster growing and metastasising (spreading to other tissues) and have a worse outlook overall; furthermore, they do not concentrate iodine and so the radio-iodine option has no role in their management.
Mrdullary carcinoma of the thyroid is an unusual type of thyroid carcinoma completely unrelated to the other types. It is derived from the so-called C-cells which normally produce the calcium lowering hormone: calcitonin.. If allowed to metastasise, it carries a bad outlook.
Thyroid lymphoma is almost invariably a high grade B cell lymphoma with a tendency to spread to other parts of the lymphoid system and bone marrow (see lymphoma section) a lower g rade B cell MALT lymphoma - which has a lower tendency to spread outside the thyroid gland.

Incidence of thyroid cancer
There is a wide variation in incidence of thyroid cancer across the world with a low incidence in the UK (circa 1 case per 100,000 of population) to high incidences such as 15 per 100,000 of population in Iceland. These differences are thought to be more due to differences in environment than to hereditary or racial causes - but see next section.
The thyroid is the only gland in the body which concentrates the salt iodine (an integral part of the thyroid hormone molecule) and the relationship between thyroid cancer incidence in iodine rich geographical regions, such as most maritime vicinities, and those with iodine lack (e.g. mountainous terrains of Switzerland – famous in the last century for its goitrous populations) has been studied with interest.

Causes of thyroid cancer
Iodine deficiency leads to the benign overgrowth of the thyroid to produce ‘goitres’ and this has led clinicians to study the relationship between environmental iodine availability and thyroid cancer. It has been demonstrated that follicular carcinoma (vide infra) is more common in regions of low environmental iodine whereas papillary carcinoma (vide infra) is as common or even more common in iodine avid as deprived regions.
Radioactive iodine pollution in the atmosphere is probably more carcinogenic and fall-out from nuclear accidents, bombs, or emissions from power stations are risks for the later development of thyroid cancer. Indeed, after exposure to nuclear fall-out containing radioactive iodine it is recommended to ingest ‘cold’ (non-radioactive) iodine to swamp the thyroid and so dilute the amount of radioactive isotope concentrated by the gland for this reason.
Total body exposure to ionising radiation of whatever source is also predisposing to thyroid cancer after an interval of some years.
Thyroid cancer is considerably more common in females than it is in males in all parts of the world, although the ratio female:male varies from 2:1 to 4:1.
There is a small incidence in childhood and then a significant incidence in young adult women before the incidence slowly and progressively rises as age increases.
There are a few very rare hereditary causes of thyroid cancer and medullary thyroid cancer (vide infra) occurs in the multiple endocrine neoplasia syndrome along with other primary tumours.
Thyroid lymphoma tends to occur in the elderly who have suffered autoimmune thyroiditis for a long time previous to the development of the lymphoma, and the inference is that the immune lymphocytes invading the gland in the benign thyroiditis have eventually turned malignant to become a lymphoma.
Anaplastic thyroid cancer (vide infra) is also a disease that tends to occur in the elderly; it is not an iodine avid cancer and therefore radioactive iodine therapy has no role (as indeed it does not in either thyroid lymphoma nor medullary cancer).
Screening for thyroid cancer
Overall, thyroid cancer is a rare disease and a population based screening programme is not indicated.
However, people with a family history of medullary thyroid cancer, MEN (multiple endocrine neoplasia) syndrome or the rare other syndromes associated with a genetic predisposition to the disease must be screened - indeed, if a patient is diagnosed with medullary cancer, it is required that the doctor rules out the inherited MEN syndrome and screens for phaeochromocytoma and hyperparathyroidism - concomitants of the inherited syndrome.
Symptoms of thyroid cancer
The patient almost invariably complains of a swelling in the neck in the thyroid region. Sometimes this is inside the thyroid gland and such lumps characteristically rise upwards towards the mouth on swallowing as the thyroid is tethered to the larynx which moves up on swallowing so taking the thyroid with it. On other occasions, the lump is in an adjacent lymph node to thyroid and indicates spread of the tumour to the neck lymph nodes. In the figure photo, one can clearly see that the young woman has a lump adjacent to her larynx on her left (but just to the right as one looks at the photo) which was indeed spread of a papillary cancer of the thyroid to a neck lymph node.
Rarely, the patient presents with breathlessness due to spread to the lungs or bone pains due to spread of the cancer to the skeleton.