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Thyroid cancer is cancer of the thyroid gland. There are four forms: papillary, follicular, medullary and anaplastic. The most common forms (papillary and follicular) are fairly benign, and the medullary form also has a good prognosis if it is restricted to the thyroid gland and a poorer prognosis if there has been spread; the anaplastic form is fast-growing and poorly responsive to therapy.

Masses of the thyroid are diagnosed by fine needle aspiration (FNA) or frequently by thyroidectomy (surgical removal and subsequent pathological examination). As the thyroid concentrates iodine, radioactive iodine is a commonly used modality in thyroid carcinomas.

Symptoms

Most often the first symptom of thyroid cancer is a nodule in the thyroid region of the neck, but only 5% of these nodules are malignant. Sometimes the first sign is an enlarged lymph node. Other symptoms that can be present are pain, changes in voice and symptoms of hypo- or hyperthyroidism.

Diagnosis

After a nodule is found during a physical examination, the most cost-effective, sensitive and accurate test to determine whether the nodule is malignant is the fine needle biopsy, which is often the initial approach without other evaluation. This test usually yields sufficient cells to assess the risk of malignancy, although in some cases, the suspected nodule is removed surgically for pathological examination, or a biopsy is done using a coarse needle, so that the arrangement of the cells can be examined (where the fine needle biopsy can only give individual cells). Blood or imaging tests may be done prior to or in lieu of a biopsy. The possibility of a nodule which secretes thyroid hormone (which is less likely to be cancer) or hypothyoidism is investigated by measuring Thyroid Stimulating hormone (TSH), and the thyroid hormones thyroxine (T4) and triiodothyronine (T3). Tests for serum thyroid autoantibodies are sometimes done as these may indicate autoimmune thyroid disease (which can mimic nodular disease). The blood assays may be accompanied by ultrasound imaging of the nodule to determine the position, size and texture, and to assess whether the nodule may be cystic (fluid filled). Some clinicians will also request technetium or radioactive iodine imaging of the thyroid.

Classification

Thyroid cancers can be classified according to their pathological characteristics. The following variants can be distinguished:

Papillary thyroid cancer

This is the most common type of thyroid cancer. It occurs more frequently in women and presents in the 30-40 year age group. It is also the predominant cancer type in children with thyroid cancer, and in patients with thyroid cancer who have had previous radiation to the head and neck (in this group, the cancer tends to be multifocal with early lymphatic spread, and portends a poor prognosis). Thyroglobulin can be used as a tumor marker for well-differentiated papillary thyroid cancer.

Pathology

Prognostic indicators
  • AGES - Age, Grade, Extent of disease, Size
  • AMES - Age, Metastasis, Extent of disease, Size
  • MACIS - Metastasis, Age at presentation, Completeness of surgical resection, Invasion (extrathyroidal), Size (this is a modification of the AGES system)
  • TNM - Tumor, node, metastasis

Surgical treatment

Arguments for total thyroidectomy are:

  • Reduced risk of recurrence
  • Papillary carcinoma is a multifocal disease (hemithyroidectomy may leave disease in the other lobe)
  • Ease of monitoring with thyroglobulin (sensitivity for picking up recurrence is increased in presence of total thyroidectomy)
  • Ease of detection of metastatic disease with thyroid scans

Follicular thyroid cancer

This occurs more commonly in women of over 50 years old. Thyroglobulin can be used as a tumor marker for well-differentiated follicular thyroid cancer.

Surgical Treatment
  • Unilateral hemithyroidectomy is uncommon due to the aggressive nature of this form of thyroid cancer.
  • Total thyroidectomy is almost automatic with this diagnosis. This is invariably followed by radioiodine treatment at levels from 100 to 200 millicuries. Occasionally treatment must be repeated if annual scans indicate remaining tissue.
  • Annual thyroid scans consist of withdrawal from thyroxine medication and/or injection of recombinant human Thyroid Stimulating Hormone (TSH). Low dose radioiodine of a few millicuries is administered. Full body nuclear medicine scan follows using a gamma camera.
  • Recombinant human TSH, commercial name Thyrogen, is produced in cell culture from genetically engineered hamster cells.

Hurthle cell variant
This type of thyroid cancer is a variant of follicular cell carcinoma with some exceptions
  • They are more often bilateral and multifocal
  • They are more likely to metastasize to lymph nodes than follicular carcinoma
  • Management - like follicular carcinoma, unilateral hemithyroidectomy is performed for non-invasive disease, and total thyroidectomy for invasive disease

Medullary thyroid cancer

This form of thyroid carcinoma originates from the parafollicular cells (C cells), which produce the hormone calcitonin. While the increased calcitonin itself is probably not harmful, it is useful as a marker which can be tested in blood. A second marker, carcinoembryonic antigen (CEA), is also produced by medullary thyroid carcinoma. It can also be measured as a serum or blood tumor marker like calcitonin. In general measurment of CEA is less sensitive than calcitonin, but has less minute to minute variability and is therefore useful as an indicator of tumor mass.

Its prognosis is poorer than that of follicular and papillary thyroid cancer when it has metastasized (spread) beyond the thyroid gland. In a proportion, approximately 25%, the cancer develops in families, both in isolated form (termed familial medullary thyroid carcinoma) or as part of the syndrome of multiple endocrine neoplasia, type 2 (MEN2), that includes medullary thyroid carcinoma (>90%), hyperparathyroidism (5-15%), and unilateral or bilateral pheochromocytoma (40-60%).

Mutations (DNA changes) of the RET proto-oncogene, a tyrosine kinase receptor involved in cell growth and development, initiate nearly all cases of hereditary or familial medullary thyroid carcinoma and are also responsible for the development of hyperparathyroidism and pheochromocytoma. It is inherited as an autosomal dominant trait, meaning that each child of an affected parent has a 50/50 probability of inheriting the mutant RET proto-oncogene from the affected parent. DNA analysis makes it possible to identify children who carry the mutant gene; surgical removal of the thyroid in children who carry the mutant gene is curative if the entire thyroid gland is removed at an early age before there is spread of the tumor. The parathyroid tumors and pheochromocytomas are removed when they cause clinical symptomatology.

Most of medullary thyroid carcinoma occurs in individuals without an identifiable family history and is assigned the term "sporadic". Individuals who develop sporadic medullary thyroid carcinoma tend to be older and to have more extensive disease at the time of initial presentation than those with a family history. Approximately 25% of sporadic medullary thyroid carcinomas have a somatic mutation (one that occurs within a single "parafollicular" cell) of the RET proto-oncogene. This mutation is presumed to be the initiating event, although there could be other as yet unidentified causes.

The major clinical symptom of medullary thyroid carcinoma is diarrhea; occasionally a patient will have "flushing" episodes, particularly with liver metastasis. This generally occurs in individuals who have a sizeable amount of tumor, most commonly having spread to the liver. Occasionally, diarrhea will be the initial presenting complaint. Sites of spread of medullary thyroid carcinoma include local lymph nodes in the neck, lymph nodes in the central portion of the chest (mediastinum), liver, lung, and bone. It may also spread to other locations, but such spread is uncommon.

After a long period during which surgery and radiation therapy formed the major treatments for medullary thyroid carcinoma, clinical trials of several new clinical agents (www.thyroidtrials.org) are now being studied. Preliminary results show clear evidence of response of a small percentage of patients, providing hope for future advances.

Anaplastic thyroid cancer

This form of thyroid cancer has a very poor prognosis (near 100% mortality) due to its aggressive behavior and resistance to cancer treatments. It rapidly invades surrounding tissues (such as the trachea).

Treatment
Unlike its counterparts, anaplastic thyroid cancer is not curable by surgery, and is in fact usually unresectable due to its high propensity for invading surrounding tissues. Treatment consists of radiation therapy usually combined with chemotherapy.

=Post-operative radiotherapy for differentiated thyroid carcinoma: when and how much
= The role of external beam radiotherapy (EBRT) in thyroid cancer remains controversial and there is no level I evidence to recommend it. No published randomised controlled trials have examined the addition of EBRT to standard treatment, namely surgery, radioactive iodine and medical suppression of thyroid stimulating hormone.

Imbalances in age, sex, completeness of surgical excision, histological type and stage, between patients receiving and not receiving EBRT, confound retrospective studies. Variability also exists between treatment and non-treatment groups in the use of radio-iodine and post-treatment thyroid stimulating hormone (TSH) suppression and treatment techniques between and within retrospective studies.

Farahati et al. and Philips et al. have reported statistically significant advantages for post operative EBRT, however, in both studies many confounding factors have been reported. For example, patients receiving EBRT were more likely to have node-positive disease, extracapsular extension and incomplete macroscopic excision. The differences in patient groups among these studies, and the difficulties with confounding factors, make evidence-based recommendations for the use of EBRT difficult to formulate. Tsang et al. have suggested a role for EBRT in patients with papillary cancer, with microscopic residual disease based on sub-group analysis showing a statistically significant advantage in terms of cause-specific survival (100% vs 95%; P=0.038) and local recurrence (93% vs 78%; P=0.01). Farahati et al. recommend the use of EBRT in node-positive patients over 40 years of age with papillary histology on the basis of an increase in time to local or distant failure (P=0.0009). Other indications for EBRT include high-grade tumours that do not concentrate iodine and tumours with gross local invasion where there is a high suspicion of microscopic or macroscopic residual disease.

The use of EBRT is controversial for those patients with microscopic residual disease. All reports on the use of EBRT have been retrospective, with varying criteria for patient selection, resulting in contradictory conclusions. Several studies have described either no or deleterious effects for EBRT, but many others have described benefit. In a study from Toronto, Brierley et al. found superior local control and improved survival in patients who received EBRT for microscopic residual disease (10-year local relapse-free rate 93% compared with 83% for patients not receiving EBRT, P = 0.01; and cause-specific survival 99% compared with 93%; P = 0.04). “Total thyroidectomy with adjuvant 131I, followed by TSH suppression is considered standard therapy for differentiated thyroid carcinoma”. In the absence of randomised data, there is credible evidence from retrospective studies (Level II-III) to recommend EBRT in addition to standard therapy in high-risk patients.

The apparent difference in outcomes related to the dose of radiotherapy is subject to the confounding factors in all retrospective studies of EBRT as outlined above. However, there are few published data that define the dose to be used. In one retrospective study, 114 patients with macroscopically resected, well-differentiated thyroid cancer were treated with EBRT and an ‘adequate’ total dose was defined as >45 Gy. Patients receiving an ‘adequate’ dose had a significantly improved local regional relapse-free survival (P<0.001). However, only three of the 114 patients in this study also received radio-iodine, and therefore the role of EBRT in addition to standard management was not examined. A total dose of 50–60 Gy was used in the two studies, which showed a reduction in local failure where EBRT was used in addition to radio-iodine (Farahatti et al., and Phillip et al.). Others have treated patients with gross residual disease with 50 Gy in 20 fractions or its equivalent and 40 Gy in 15 fractions or its equivalent in the presence of microscopic residual disease. If the decision is made to treat a large volume, including the cervical nodes for instance, or if there is extracapsular extension and local invasion of cervical nodes, fractionation is changed to 2 Gy fractions. Currently, recommended doses are 50 to 60 Gy in 25 to 30 fractions over 5 to 6 weeks.

To treat the thyroid bed, a clinical target volume from the hyoid to suprasternal notch is determined. A simple technique is to use two antero-lateral oblique wedged fields, or direct electron beams. When using oblique fields the posterior border is placed to exclude the spinal cord. If it is determined that the clinical target volume should include the cervical and superior mediastinal lymph nodes, as well as the thyroid bed, a two-phase technique is commonly used. The initial volume (phase I) includes the regional lymph nodes from the mastoid tip to the carina, including the thyroid bed. The phase I volume may consist of parallel opposing antero-posterior/postero-anterior fields to 40–46 Gy. The phase II volume should include the tissues considered at highest risk of relapse, aiming to boost the high-risk area to a total dose of 14 Gy (cumulative total dose of 60 Gy). For the boost to the thyroid bed alone, several techniques can used, such as, a direct anterior electron beam, antero-lateral oblique wedge fields, or a lateral pair of angled-down oblique fields, achieved with a couch rotation of 10–20 degrees, aiming inferiorly to avoid the shoulders, off the spinal cord. Since the thyroid bed target volume is wrapped around many critical structures in the neck and it is often necessary to include regional lymph nodes, treatment planning of this difficult volume is ideal for conformal radiotherapy, or intensity-modulated radiation therapy. A conformal plan may be used either to treat the thyroid bed alone or to include the cervical nodes.

Recommended indications for the use of EBRT are:

  1. High Grade tumors that do not concentrate radio-iodine.
  2. Recommendations for EBRT after 131I therapy include high-risk patients defined as; older (>45 years) with potential microscopic residual disease, after resection of gross extrathyroid extension (i.e. UICC 6th edition category T4a or T4b but not T3), or multiple lymph-node involvement.
  3. Bulky tumors with superior mediastinal / retro-sternal extension.
  4. Gross evidence of local invasion at surgery and presumed to have significant macro or microscopic residual disease, particularly if there is residual tumour that fails to concentrate 131I and is apparent only by raised thyroglobulin.
  5. For locally advanced tumors which are inoperable for a variety of lesions it can be used for palliation along with TSH suppression.
  6. For recurrent disease in the neck which is not amenable to radio-iodine therapy or further surgery.
  7. For palliation of recurrent disease or metastatic disease in bone, cerebrum, spine and other areas.

=Adjuvant therapy for medullary thyroid cancer
= Unlike differentiated thyroid carcinoma, there is no role for radioiodine treatment in medullary-type disease. External beam radiotherapy should be considered for patients at high risk of regional recurrence, even after optimum surgical treatment. Brierley et al., conducted a retrospective study of the treatment given to patients with microscopic residual disease, extraglandular invasion, or lymph-node metastases and found the locoregional relapse-free rate at 10 years was 86%, compared with 52% for those patients who did not receive adjuvant therapy. Typically, 40 Gy is given in 20 fractions to the cervical, supraclavicular, and upper mediastinal lymph nodes for 4 weeks, with subsequent booster doses of 10 Gy in five fractions to the thyroid bed, especially in the setting of gross residual disease.

=Adjuvant therapy for anaplastic thyroid cancer
= Treatment of anaplastic-type carcinoma is generally palliative in its intent for a disease that is rarely cured and almost always fatal. The median survival from diagnosis ranges from 3 to 7 months, with worse prognosis associated with large tumours, distant metastases, acute obstructive symptoms, and leucocytosis. Death is attributable to upper airway obstruction and suffocation in half of patients, and to a combination of complications of local and distant disease, or therapy, or both in the remainder. In the absence of extracervical or unresectable disease, surgical excision should be followed by adjuvant radiotherapy. In the 18–24% of patients whose tumour seems both confined to the neck and grossly resectable, complete surgical resection followed by adjuvant radiotherapy and chemotherapy could yield a 75–80% survival at 2 years.

References

See also

External links

Oncology | Otolaryngology | Thyroid disease | Types of cancer

Schilddrüsenkrebs | Tumori della tiroide | Tumor da tiróide | Thyroid cancer | Kilpirauhassyöpä | Thyroideacancer | Ung thư tuyến giáp

 

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