Thyroid cancer symptoms
Although thyroid cancers are the most common endocrine malignancy, they are generally uncommon, accounting for <1% of all cancers and <0.5% of all cancer deaths, with an annual incidence of approximately 2.3 per 100 000 women and 0.9 per 100 000 men. Papillary carcinoma presents in patients between the second and third decades, follicular carcinoma tends to present in older patients, and anaplastic carcinoma tends to present in patients in the sixth and seventh decades.
There are four main types of thyroid cancer: papillary, follicular, anaplastic and medullary thyroid carcinoma. Exposure to radiation, nuclear fall-out and neck irradiation are considered to be important risk factors in the development of thyroid cancer.
Papillary carcinoma is the most common (70-80%), with a 3:1 female preponderance, and is derived from thyroid follicular cells. The main method of spread is via the lymphatic system, 30% can be multifocal.
Follicular carcinoma also comes from thyroid follicular cells and makes up 10-15% of thyroid cancers, with a 2:1 female preponderance. It is more aggressive than papillary carcinoma and commonly spreads (in 10-15% cases)to lungs and bones via the blood stream. Hürthle cell carcinoma is an aggressive follicular tumour with a worse prognosis
Anaplastic carcinoma is uncommon, comprising less than 10% of thyroid cancers, with a slight male preponderance, 1.5:1. It is also known as undifferentiated carcinoma because the histological appearance of the cells does not resemble normal thyroid tissue. Anaplastic carcinoma is extremely aggressive and spreads rapidly via local invasion, through the lymph nodes and blood stream.
Medullary carcinoma makes up about 5-10% of thyroid cancers. It arises from the parafollicular C cells that produce calcitonin. It can lead to a wide variety of biochemical derangements. Amyloid is sometimes found in specimens of medullary carcinoma. Most medullary carcinomas are sporadic but some are familial and others are associated with multiple endocrine neoplasia type 2
.Scope of disease
Patients with recent or expanding growth of a thyroid carcinoma may present with a palpable nodule. Infiltration into the recurrent laryngeal nerve leads to hoarseness of voice.
Each tumour type has its own predilection for metastatic spread. Papillary carcinoma tends to spread via the lymphatics to the lymph nodes, follicular carcinomas tend to spread via the blood stream into the lungs and liver, and anaplastic carcinoma can spread via the lymphatics and blood stream.
Patients with medullary carcinoma may develop features related to ectopic production of hormones such as ACTH (Cushing's syndrome), serotonin, vasointestinal peptide (VIP; flushing and diarrhoea) and calcitonin, which can be used as tumour markers.
Thyroid cancer usually presents as a lump (solitary or multinodular) in the neck, in a clinically euthyroid patient with no other symptoms.
When assessing a patient with a thyroid nodule, it must be borne in mind that the vast majority of such nodules are benign. Features that increase the likelihood of malignancy include a family history of cancer, previous neck irradiation, a rapidly growing nodule, hoarseness or change in voice, swollen lymph nodes, difficulty swallowing and stridor. Rarely, patients may present with signs or symptoms of metastatic disease such as pathological fractures from bony metastases.
Thyroid-stimulating hormone and free T4
Patients with thyroid cancer usually have normal thyroid function tests.
In the majority of patients with a thyroid nodule, fine-needle aspiration is the first and only test required. This involves multiple passes of a needle into the nodule while aspirating into a syringe. The cells are then stained and examined under a microscope, and then classified into categories ranging from benign to suspicious to definitely malignant.
Fine-needle aspiration has superseded the need for the majority of iodine-131 or technetium-99m labelled pertechnetate scans. Currently radionuclide scans are reserved for patients in whom fine-needle aspiration is non-diagnostic. Classically, malignant nodules are non-functional and appear as cold spots , whereas nodules from toxic adenoma appear as hot spots. Unfortunately, up to 8% of hot and 16% of cold nodules may be malignant.
Serum calcitonin and carcino-embryonic antigen (CEA)
Calcitonin and CEA are measured if there is clinical suspicion of medullary carcinoma.
A screening chest X-ray should be performed to detect lung metastases.
Ultrasound of the thyroid
High-resolution ultrasound of the thyroid can differentiate between diffuse and focal disease, capsular invasion and local lymph node enlargement. It can also be used to direct fine-needle aspiration.
CT or MRI of the neck and chest
Further imaging may be required in patients in whom the borders of the goitre cannot be clearly defined, or where there is a fixed lump.
The extent of surgery ranges from a lobectomy to a total thyroidectomy . However, the absence of controlled clinical studies in papillary and follicular carcinoma means that there is no consensus on the exact level of surgical resection and the need and extent of regional lymph node dissection. In general, total or near-total thyroidectomy is recommended for most thyroid carcinomas. Limited surgery in the form of a total lobectomy may be used in papillary or follicular carcinomas in low-risk patients with tumours less than 1 cm.
Treatment of medullary carcinoma is with total thyroidectomy and complete regional neck lymph node dissection. Surgery is not recommended in anaplastic carcinoma unless airway obstruction is imminent.
The debate about extent of surgery arises because the complications of a near-total or total thyroidectomy need to be weighed against the benefits. Advocates of total thyroidectomy cite advantages such as eliminating the possibility of recurrence from a bilateral cancer, facilitating the use of postoperative radio-iodine therapy, which is difficult to administer with the residual thyroid lobe in situ, and monitoring of recurrences. Advocates of less than total thyroidectomy claim that well-differentiated tumours carry a good prognosis in general, that results of a lobectomy are similar to total thyroidectomy, and that the present use of adjuvant therapy is still undefined.
Radioactive iodine (131I) can be used as adjuvant therapy after surgery to ablate residual thyroid tissue in patients with follicular or papillary carcinomas. Thyroid replacement therapy is given to these patients after thyroidectomy. The purpose is to replace any thyroid hormone deficiency and to suppress the TSH so that any remaining cancer cells are not stimulated to grow. Metastatic disease can alsobe treated with radioactive iodine. There is no role for radioactive iodine in medullary carcinoma because the C cells do not take up iodine.
External beam radiotherapy
Patients with anaplastic carcinoma do not derive substantial benefit from surgery or radioactive iodine; the primary treatment for them is external beam radiotherapy. Metastatic disease can also be treated with external beam radiotherapy.
Mortality of patients depends on the type of cancer, stage and risk category. Patients with a single isolated nodule that responds well to therapy have a 5-year survival probability of more than 90%. In general, the prognosis is better for patients with papillary carcinoma rather than the follicular carcinoma.
In contrast, patients with anaplastic carcinoma and metastasis at presentation have a 5-year survival probability of less than 10%. The overall median survival of patients with anaplastic carcinoma is about 6 months.
Patients with medullary carcinoma have survival rates of about 60% at 10 years.
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