The thyroid cancer

The thyroid cancer usually develops in the form of a nodule in the thyroid gland it is normal or increased in size (goiter). This is a rare cancer, most common in young patients with good prognosis in papillary form since healing occurs in 90% of cases.

 Epidemiology
The thyroid cancer is a rare cancer. It represents approximately 1% of cancers occurring in the general population in France. Its annual incidence is low or about 2.5 per 100 000 people.

The network "Francim" cancer registries set up to monitor the incidence and analyze the role of the Chernobyl accident, has made an update of data on thyroid cancer. This update covering the period 1978-1997 indicates in particular that the increase in thyroid cancer is about 6.2% per year in men and 8.1% per year in women.

The prevalence of thyroid nodules is variable according to the means testing. It is more common in women, the elderly, individuals living in areas of iodine deficiency or who have undergone irradiation of the neck during childhood but these nodules are benign in more than 90% of cases. Young subjects are more susceptible to cancer because of greater sensitivity of the thyroid to radiation.

 Classification

The classification of the disease is important because of its determination follows the diagnostic and therapeutic approach.
1 / TNM Classification

Primary tumor:

T0: no palpable tumor
T1: tumor limited to a single lobe or the isthmus, mobility intact, no deformation of the gland
T2: single or multiple tumor distorting the gland intact mobility
T3: tumor beyond the gland or fixed or infiltration device

Cervical lymphadenopathy:

N0: no palpable lymphadenopathy
N1: one or more lymph nodes, palpable, mobile, ipsilateral
N2: contralateral lymph and / or bilateral, mobile
N3: One or more nodes attached

Visceral metastases:

M0: no metastases detectable
+ M: metastasis detected

2 / histological classification

Following the international histological classification, there are four main histological types of thyroid carcinoma:

The papillary carcinomas,
the follicular carcinomas (or follicular, Anglo-Saxon term)
the medullary carcinomas,
the squamous anaplastic (or undifferentiated).
These tumors may be solitary or multifocal.

Papillary cancers are more common. They predominate in young subjects and about 80% of thyroid cancers.

Gallbladder cancers represent about 10% of thyroid cancers and are especially common around the quarantine.
Papillary and follicular cancers represent the group of differentiated thyroid cancers radiosensitive. They secrete thyroglobulin.

Medullary cancers account for 5% of thyroid cancers and correspond to a tumor or parafollicular C cells derived from neural crest. C cells secrete calcitonin, which the immunoassay in plasma is an excellent marker for this cancer.

Undifferentiated or anaplastic cancers are rare (less than 5% of cases) and extremely serious.

There are other much less common histological types: squamous metaplastic squamous, connective sarcoma, lymphoma ...

 Risk Factors

Sources: Institut de Veille Sanitaire - Epidemiological surveillance of thyroid cancers.

The risk factor most recognized is that of external irradiation of the thyroid gland in adulthood and childhood. Other factors were mentioned but none of them has clearly established a causal role in thyroid cancers. It was noted in particular:

The endemic goiter by iodine deficiency.
Food: the risk increased slightly by eating fish or shellfish in areas without iodine deficiency. Crucifers contain compounds that can interfere with thyroid metabolism.
Some drugs, such as pentobarbital, griseofulvin, spironolactone, have been implicated in thyroid cancer.
Occupational factors: it was noted an increased risk for certain occupations exposed to X-rays, and in women of fishermen in Norway (consumption of fish or seafood).
Individual factors: hormonal and reproductive factors in women - thyroid disease (the presence of a goiter or thyroid nodules is strongly associated with risk of thyroid cancer, Hashimoto's thyroiditis also seems to be a predisposing factor for lymphoma thyroid).
Family factors: familial forms of cancer are well described for the rare forms of medullary thyroid cancer, as part of MEN syndrome (multiple endocrine neoplasia).
 Diagnosis

The most frequent clinical form of thyroid cancer is the single thyroid nodule. The diagnosis is based on nodule palpation neck that will search for items suspected of malignancy as an irregular, hard nodule.
Palpation can also provide information on the shape and volume of the thyroid gland, to assess the consistency of the thyroid tissue, its potential sensitivity, and mobility training in relation to the thyroid tissue adjacent. The cervical lymph nodes and supraclavicular must be systematically examined.

In addition to the history and palpation, the differential diagnosis is done using the diagnostic tests:

Laboratory tests. The dosage of thyroid stimulating hormone (TSH) gives indirect information on thyroid function. Calcitonin is a good marker of medullary thyroid cancer type.
The fine needle aspiration cytology (CAF). Performed by an experienced cytologist is examining the most reliable and least invasive to distinguish malignant nodules from benign nodules with a specificity and sensitivity of 95%.
Ultrasound allows the description of a suspected nodule on palpation: situation in the gland, measurements, solid character, fluid or mixed echogenicity, an isolated or combined with other nodules.
Scintigraphy is indicated when there are signs of hyperthyroidism, in search of a toxic nodule. It is not necessary when the nodule is infracentimétrique.
 Treatments

1 / surgery

In the presence of a malignant thyroid nodule, the basic treatment is surgery. Shall include at least the removal of the lobe bearing the lesion and adjacent isthmus. Treatment of medullary thyroid cancer requires a specific act consisting of total thyroidectomy with at least one of the central compartment lymph node dissection. In all cases, these actions must be performed by a surgeon trained. Complications, hypoparathyroidism or laryngeal paralysis are rare.

2 / I-131

If he persists in the residual functional tissue, a dose of 1.11 to 3.7 GBq (30-100 mCi) of iodine-131 is administered in single room, 4 to 6 weeks after total thyroidectomy, in order to sterilize all.
40% of metastases of thyroid cancers bind iodine and can be treated by this method.

3 / hormone therapy

After total thyroidectomy and sterilization of the thyroid with iodine-131, is administered thyroxine, a hormone inhibiting the secretion of TSH. The dosage is 100 to 200 mg / day following the patient's clinical status.
This hormone also helps to ensure an adequate balance in terms of thyroid function.

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