出典(authority):フリー百科事典『ウィキペディア(Wikipedia)』「2013/12/31 00:29:18」(JST)
Papillary thyroid cancer | |
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Classification and external resources | |
Papillary thyroid carcinoma.
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ICD-10 | C73 |
ICD-9 | 193 |
ICD-O: | M8260/3 |
OMIM | 603744 |
MedlinePlus | 000331 |
eMedicine | med/2464 |
MeSH | D013964 |
Papillary thyroid cancer or papillary thyroid carcinoma[1] is the most common type of thyroid cancer,[2] representing 75 percent to 85 percent of all thyroid cancer cases.[1] It occurs more frequently in women and presents in the 20–55 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.[3]
Thyroglobulin can be used as a tumor marker for well-differentiated papillary thyroid cancer.[4][5] HBME-1 staining may be useful for differentiating papillary carcinomas from follicular carcinomas; in papillary lesions it tends to be positive.[6]
Although papillary carcinoma has a propensity to invade lymphatics, it is less likely to invade blood vessels.[14] These kinds of tumors are most commonly unencapsulated, and they have a high tendency to metastasize locally to lymph nodes, which may produce cystic structures near the thyroid that are difficult to diagnose because of the paucity of malignant tissue.[15] Furthermore, papillary tumors may metastasize to the lungs and produce a few nodules or the lung fields may exhibit a snowflake appearance throughout.
Other characteristics of the papillary carcinoma is that E.M. shows increased mitochondria, increased RER, as well as increased apical microvilli. Moreover, papillary carcinomas have an indolent growth, and 40 percent of cases spread out of the capsule.[16]
Mutations associated with papillary thyroid cancer are mainly two forms of chromosomal translocation and one form of point mutation. These alterations lead to activation of a common carcinogenic pathway—the MAPK/ERK pathway.
Chromosomal translocations involving the RET proto-oncogene (encoding a tyrosine kinase receptor that plays essential roles in the development of neuroendocrine cells) located on chromosome 10q11 occur in approximately a fifth of papillary thyroid cancers. The fusion oncoproteins generated are termed RET/PTC proteins (ret/papillary thyroid carcinoma), and constitutively activate RET and the downstream MAPK/ERK pathway.[1] The frequency of ret/PTC translocations is significantly higher in papillary cancers arising in children and after radiation exposure.[1] The gene NTRK1 (encoding the TrkA receptor), located on chromosome 1q, is similarly translocated in approximately 5 percent to 10 percent of papillary thyroid cancers.[1]
Approximately a third to a half of papillary thyroid carcinomas harbor point mutations in the BRAF oncogene, also activating the MAPK/ERK pathway.[1] In those cases the BRAF mutations found were V600E mutation. After performing a multivariate analysis, it was found that the absence of tumor capsule was the only parameter associated (P=0.0005) with BRAF V600E mutation.[15] According to recent studies, papillary cancers carrying the common V600E mutation tend to have a more aggressive long term course. BRAF mutations are frequent in papillary carcinoma and in undifferentiated cancers that have developed from papillary tumors.
Papillary thyroid carcinoma is usually discovered on routine examination as an asymptomatic thyroid nodule that appears as a neck mass. In some instances, the mass may have produced local symptoms. This mass is normally referred to a fine needle aspiration biopsy (FNA) for investigation. FNA accuracy is very high and it is a process widely used in these cases. Other investigation methods include ultrasound imaging and nuclear scan. The ultrasound is a useful test to distinguish solid from cystic lesions and to identify calcifications.[17] The thyroid ultrasound is also very effective to discover microcarcinomas, which refer to very small carcinomas (<1 cm).
Papillary thyroid carcinomas are also discovered when a hard nodule is found in multinodular goiter, when enlarged cervical lymph nodes are detected, or when there are unidentified metastatic lesions elsewhere in the body.[15] Expanding lesions found in the thyroid gland, especially if they are painful, should be examined as they may indicate the presence of papillary thyroid carcinoma. Other clinical signs that could indicate papillary thyroid are: fixation to the trachea, stony hardness, damage to recurrent laryngeal or cervical sympathetic nerves. Seventy five percent of the population will have these thyroid nodules, and the majority will always be benign.[18]
Chest x rays are not commonly performed. In cases of metastasis, some other tests are run to obtain sufficient information before a surgery. Such tests include the ultrasound and MRI of the neck as well as the CAT scanning. Other options that have shown good results in identifying tumors or related outcomes are the use of thallium-201 chloride, which helps identify metastatic tumor; gallium scan, which is helpful to visualize lymphomas; I-metaiodobenzylguanidine (MIBG) which has proven useful in imaging MTC; Tc-MIBI, which has been effective in detecting deposits of metastatic thyroid cancer; PET scans, which are also helpful for the imaging of metastatic disease. Chia et al. report that TSHR mRNA measured with FNA enhances the preoperative detection of cancer in patients with thyroid nodules, reducing unnecessary surgeries, and immediate postoperative levels can predict residual/metastatic disease.[15] Suspected lung metastases and/or miliary aspects at x-ray or CT can be diagnosed by cytology on a bronchoalveolar lavage specimen.[19]
Depending on source, the overall 5-year survival rate for papillary thyroid cancer is 96 percent[20] or 97 percent,[21] with a 10-year survival rate of 93 percent.[20]
For a more specific prognosis for individual cases, there are at minimum 13 known scoring systems for prognosis; among the more often used are:
The MACIS system of estimating the prognosis of papillary thyroid cancer was developed by Clive S. Grant at the Mayo Clinic, and was based on careful evaluation of a large group of patients. It is probably the most reliable staging method available.[23]
It assigns scores to the main factors involved, and uses the sum of this score to calculate the prognosis:
Factors[23] | Score[23] | |
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Distant Metastasis: spread of the cancer to areas outside the neck | Yes | 3 |
No | 0 | |
Age at the time the tumor was discovered | Less than 39 years | 3.1 |
Over 40 years | 0.08 x age | |
Invasion into surrounding areas of the neck as seen by the naked eye | Yes | 1 |
No | 0 | |
Completeness of surgical resection (or removal) of the tumor | Incomplete | 1 |
Complete | 0 | |
Size of the tumor | 0.3 x size in cm |
Sum of MACIS score[23] | 20 yr Survival[23] |
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< 6.0 | 99% |
6.0 - 6.99 | 89% |
7.0 - 7.99 | 56% |
> 8.0 | 24% |
Most patients fall into the low risk category (MACIS score less than 6.0) and are cured of the cancer at the time of surgery.[23]
Children with multiple lung metastases and/or a miliary aspect still have an excellent long-term prognosis if given adequate treatment.[19]
Based on overall cancer staging into stages I to IV, papillary thyroid cancer has a 5-year survival rate of 100 percent for stages I and II, 93 percent for stage III and 51 percent for stage IV.[24]
Surgical treatment:
Arguments for total thyroidectomy are:
Thyroid total body scans are less reliable at finding recurrence than TG and ultrasound.
Papillary tumors tend to be more aggressive in patients over age 45. In such cases it might be required to perform a more extensive resection including portions of the trachea. Also, the sternocleidomastoid muscle, jugular vein, and accessory nerve are to be removed if such procedure allows apparently complete tumor resection. If a significant amount of residual tumor is left in the neck, external radiotherapy has been indicated and has proven useful especially in those cases when residual tumor does not take up radioiodine.
After surgical thyroid removal, the patient waits around 4–6 weeks to then have radioiodine therapy. This therapy is intended to both detect and destroy any metastasis and residual tissue in the thyroid. The treatment may be repeated 6–12 months after initial treatment of metastatic disease where disease recurs or has not fully responded.[25]
Patients are administered hormone replacement levothyroxine for life after surgery, especially after total thyroidectomy. Chemotherapy with cisplatin or doxorubicin has proven limited efficacy, however, it could be helpful for patients with bone metastases to improve their quality of life. Patients are also prescribed levothyroxine and radioiodine after surgery. Levothyroxine influences growth and maturation of tissues and it is involved in normal growth, metabolism, and development. In case of metastases, patients are prescribed antineoplastic agents which inhibit cell growth and proliferation and help in palliating symptoms in progressive disease.
After successful treatment, 35 percent of the patients may experience recurrence within a 40-year span. Also, patients may experience a high incidence of nodule metastasis, with 35 percent cases of cervical node metastases. Approximately 20 percent of patients will develop multiple tumors within the thyroid gland.[26]
Micrograph of papillary thyroid carcinoma demonstrating prominent papillae with fibrovascular cores. H&E stain.
Micrograph showing that the papillae in papillary thyroid carcinoma are composed of cuboidal cells. H&E stain.
Micrograph (high power view) showing nuclear changes in papillary thyroid carcinoma (PTC), which include groove formation, optical clearing, eosinophilic inclusions and overlapping of nuclei. H&E stain.
Micrograph (high power view) of PTC demonstrating nuclear clearing and overlapping nuclei. H&E stain.
Micrograph of metastatic papillary thyroid carcinoma to a lymph node. H&E stain.
Micrograph of papillary thyroid carcinoma, tall cell variant - high magnification. H&E stain.
Micrograph of papillary thyroid carcinoma, tall cell variant - intermediate magnification. H&E stain.
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リンク元 | 「甲状腺乳頭癌」 |
関連記事 | 「papillary」「thyroid」「papilla」 |
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