The Thyroid Gland And Thyroid Cancer Biology Essay

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Papillary Thyroid Carcinoma accounts for 70 to 80 of thyroid cancer and is also the most common form of thyroid cancer. Papillary is a malignant neoplasm that is developed by the follicle cells, these are characterized as fingerlike projection that have a fine

chromatin pattern that is associated with nuclear grooves. This type of tumor is typically irregular or solid masses. This type of thyroid cancer is normally a slow growth pattern that has propensity with lymphatic invasion and lymph node metastasis in the neck.

        There are several different PTC and each can be differentiated microscopically. Some forms of PTC are due to DNA mutations that are results over activation or specific damage to the parts of the BRAF or RET genes. These types of DNA mutations are not inherited; they are

acquired throughout a person's lifetime. Due to ACS this form of the RET gene that is known as PTC is reported that the mutation of the BRAF gene has been found in about 30% to 70% of the patients with PTC. A lot of the patients either have the RET or BRAF mutation but never

both. The cells from PTC can be spread quickly into the cervical lymph nodes. Although PTC cells can spread quickly they are treated easily and are unlikely to become fatal.

        The primary treatment for PTC is a complete thyroidectomy especially if the tumor is bigger than 1 cm in diameter or if it has a metastasized. The reason behind a total thyroidectomy instead of a partial one or a lobectomy is due to the fact that majority of the patients that have PTC (60% to 85%) show lesions in both the lobes, and there is a 5% to 10 % recurrence rate for a lobectomy.

Another form of thyroid cancer is the Follicular Thyroid Carcinoma (FTC). Follicular is the second most common cancer which makes up 20% of thyroid cancers. This type of cancer has a follicular pattern and it is characterized by a coarse chromatin pattern. Follicular Thyroid Carcinoma has a tendency to metastasize to the brain, bladder, bones, skin and lungs; it rarely goes to the lymph nodes. About 25% of FTC patients end up developing metastases during the follow-up period. Hurtle cell carcinoma is a subtype of FTC and it accounts for 4% of thyroid cancers. HCC is difficult to treat due to it not being able to respond well to radioactive iodine treatment. Hurthle cell carcinoma has a pattern of metastasis which includes both locoregional invasion and distant metastases. About 35% of patients with HCC have metastases. Even though the use of tumor markers to differentiate different types of papillary thyroid carcinoma has been useful and quite well documented, it's more difficult to differentiate follicular thyroid carcinoma from adenoma.  Some of the tumor markers that have been identified for this test are Galactin-3, Dipeptidyl amino peptidase IV activity, PAX8/MIB-1, Core 1 Gene, HBME-1 which are a combination of p53 expression in a nucleus, and Bc2 in a cytoplasmic immunoreactivity and membranous CD44V6 staining.  Most promising targets for immunocytodiagnosis are the galactin-3 and CD44V6 which have a functional role in growth of the tumor and progression of the tumor.  The primary treatment for FTC is surgery because Follicular is not multicentric.

        Medullary Thyroid Carcinoma is responsible for about 3% of thyroid cancers. This type of cancer is a soft malignant neoplasm in the epithelium that contains little or no fibrous tissue. Some of the patients with this type of cancer present with symptoms such as diarrhea, flushing and painful bine metastases. Constipation, depression, marfanoid body habitus are syndromes that are associated with MTC that might initiate diagnostic testing for this type of cancer. Medullary is the only type of cancer that develops from C cells of the thyroid gland. This type of neoplasm releases the hormone calcitonin and the protein carcinoembryonic antigen into the

bloodstream, which can be tested by blood tests. MTC is not responsive to chemotherapy or conventional radiation therapy, so early diagnosis and treatment is very important for a patient's survival. Sporadic and familial are two types of MTC that can be associated with many

different varieties of symptoms. Sporadic makes up 85% of cases and are usually found in older adults in only one thyroid lobe. Changes in the RET genes within the cancer cells are found in approximately one out of every five patients that have sporadic MTC.

        The familial form of MTC occurs in each generation of a family that is carrying the genetic mutation. Mutation is found in every cell of the patient's body which can be inherited and tested through DNA; unlike the RET mutation which is only found in cancer cells. Inherited MTC cancers are often developed and are spread through early life and become more aggressive than the form of sporadic MTC. Isolated familial medullary thyroid carcinoma (FMTC) are different form of familial and is the only type of cancer that is found in the family or has 2 multiple endocrine neoplasia; which is when FMTC and other certain forms of cancer is found in the family.

        One last type of thyroid cancer is the Anaplastic Thyroid Carcinoma, which is also called undifferentiated thyroid carcinoma. Anaplastic is a rare cancer and makes up only 2% of all thyroid cancers. In research it shows that this form is developed through an existing

papillary or follicular cancer. Anaplastic is very aggressive and invades the neck and spreads to other parts of the body quickly such as bone, brain, lungs, and pleura. The death results of this cancer are upper airway obstruction and suffocation in about half of the patients that are diagnosed with anaplastic thyroid cancer. Death results also have a combination of complications due to the disease itself and or the therapy. Surgical biopsy, CT exams of the

mediastinum and neck is how you diagnose this type of cancer; it shows the extent of the tumor invasion of aero digestive structures. Radiographs show pulmonary metastases that show nodules and or bone metastases that appear to look like lytic lesions.

        There are two types of research methods to understand the pathogenesis of anaplastic. Comparative genomic hybridization (CGH) detects changes in the cell line of the chromosomal makeup. Research is being in process to identify genes that are responsible for the transformation of anaplastic and that could eventually improve accuracy of prognosis and lead to a genetic therapy later on in life. The intersimple sequence technique repeats polymerase chain reaction that is used to show the genetic fingertips of anaplastic and

papillary carcinomas that occurs in the same thyroid share similarities which indicates that anaplastic grows from papillary. The treatment is pretty much palliative in which the median survival from time of a patient being diagnosed is 3 to 7 months. Increasing in size of tumor, acute obstructive symptoms, presence of distant metastases and leukocytosis worsens the prognosis. The primary treatment for anaplastic is surgical excision and external beam radiation

therapy.

        There are many ways to stage thyroid cancer, but I will inform you about the first three I have read about. AGES, Clinical Class, and AMES are three different ways to stage thyroid cancer. The AGES system was published by Hay ET all in 1987 at the Mayo Clinic. This system uses age, tumor grade, tumor size for assessment, and extent of the disease. AGES is difficult to apply to patients that have DTC because often pathologists do not report the tumor grade with follicular and papillary thyroid carcinomas. The second stage is Clinical class which has been applied to PTC or FTC patients in separate studies. The Clinical class system was created at the

University of Chicago in 1980s by DeGroot and his colleagues which categorized it into 4 classes that were based on anatomical extent of the tumor. The tumor that was contained in the thyroid gland is called Class 1, those that are involved by the cervical lymph node is

considered Class 2, class 3 is when the extrathyroidal tumor is invading and Class 4 indicated by the presence of distant metastases. The original study of patients with PTC (8.2%) died within 12 years after diagnosis.

        The third system is AMES which was developed in the 1980s using the data from 814 patients that had DTC. In this system age and size were used to categorize variables which separated patients into high and low-risk groups. The low-risk group had men who were younger than 41 and women that was younger than 51 that did not have distant

metastases and those who were older but had intrathyroidal PTC or had minimal invasion of FTC and had a tumor less than 5 cm that did not have distant metastases. In this study the authors reported that 1.8% - 46% had mortality rates and lived at 13 years. Radioiodine cintigraphy and ultrasonography have been the imaging modalities that are most commonly used lately to visualize thyroid cancer. At the moment PET-CT (positron emission tomography and computed tomography) is approved to use assessing suspected recurrence of differentiated thyroid cancer in patients that had radioiodine negative scan and also had detectable thyroglobulin (tg) levels.

        As you see thyroid cancer is most common than other cancers. You can also see that each year the amount of those diagnosed with some type of thyroid cancer is increasing. More treatments are being researched and having a physical exam for signs of cancer is very important to catch it early so the less serious procedure can be done.

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