By Saman J. Ansari, Islamabad
We have all heard of various diseases associated with thyroid like goiter, hyperthyroidism and hypothyroidism etcetera. Cancer of thyroid gland or thyroid carcinoma is uncommon yet it comprises of 1-2% of all human cancers and is the most frequent endocrine malignancy.
The thyroid gland is an endocrine gland and is the largest gland in the neck. It is situated in the anterior neck below the skin and muscle layers. Its function is to regulate body’s metabolism. The thyroid gland has two main type of cells; follicular and parafollicular.
Thyroid cancer arises from thyroid follicular cells (papillary, follicular and anaplastic) or from other cells within the thyroid gland like lymphocytes (primary thyroid lymphoma) or neuroendocrine C cells (medullary thyroid carcinoma). Formation of lumps in the gland is called thyroid nodules. 1 in 20 out of these nodules becomes malignant and thus become cancerous.
Thyroid cancer typically doesn’t cause any signs or symptoms early in the disease. As thyroid cancer grows, it may cause a lump that can be felt through the skin on the patient’s neck, voice become hoarse, difficulty swallowing, pain in neck and throat and swollen lymph nodes in neck.
Thyroid cancer is a relatively rare neoplasm worldwide, accounting for approximately 1–5% of all cancers in females and less than 2% in males. Incidence rate in Asia is comparatively lower than rest of the world, the highest being in Europe and the lowest in Africa. In Pakistan thyroid cancer is responsible for 1.2% cases of all malignant tumors. Papillary thyroid carcinomas are the most widespread ranging from 69-71% followed by follicular carcinomas from 11.6-13%.
RISK FACTORS OF THYROID CANCER
Exposure to ionizing radiation (IR) is a common risk factor for cancer. The thyroid may be irradiated more than other tissues because of its position in the body and its ability to concentrate iodine. The thyroid is very radiosensitive at a young age. Children exposed to radiation frequently develop papillary thyroid cancer (PTC). Therefore, thyroid carcinoma is more common in children.
Another specific source of thyroid irradiation is thyroid imaging with 131I that has been largely used for the diagnosis of thyroid diseases. Finally, radiotherapy for head and neck malignancies is an additional source of thyroid irradiation.
TSH Levels and Iodine Intake
Iodine deficiency causes an increase of thyroid-stimulating hormone (TSH), a major growth factor for thyroid follicular cells. Iodine intake is known to influence the thyroid cancer histotype distribution, rather than the overall incidence, with more follicular and fewer papillary carcinomas in iodine-deficient areas. When iodine as a treatment is used, average serum TSH decreases and the papillary: follicular ratio increases.
As obesity is a syndrome with many factors, the contribution to carcinogenesis of each single obesity feature (type of adiposity, metabolic derangement, insulin resistance, etc.) is unclear. A recent study supports the possibility that insulin resistance and hyperinsulinemia (a typical feature of obesity) rather than metabolic derangement may be a risk factor for thyroid cancer.
Lifestyle and Environmental Pollutants
Dietary intake and lifestyle may significantly change in the same individual over time. Some industrialized food contaminants, for instance nitrates, can compete with iodine uptake by the thyroid and can behave as potential thyroid function disruptors and carcinogens. Nitrate is a frequent contaminant of drinking water in areas of intense agricultural industry and is found at high levels in some vegetables and processed food. A high average nitrate level in water supplies is associated with an increased risk of thyroid cancer.
In the last decades, the population has been more exposed to environmental pollutants like asbestos, benzene, formaldehyde, pesticides, bisphenol A (BPA), polychlorinated biphenyls (PCB), and polyhalogenated aromatic hydrocarbons (PHAHs), all compounds that may act as either genotoxic or non-genotoxic carcinogens.
Out of 80,000 chemicals present in products on the US market, only a few hundred have been tested for carcinogenicity, and their possible combinations provide an indefinite number of potential carcinogens. It is possible that some products have a specific carcinogenic effect on the thyroid, either directly or acting as endocrine disruptors. It is need of the hour that Pakistani pollutants too are tested for their potential carcinogenic effect.
Initiation and progression of thyroid cancer also involves multiple genetic and epigenetic alterations. Mutations leading to the activation of the MAPK and PI3K–AKT signaling pathways are crucial. Common mutations found in thyroid cancer are point mutation of the BRAF and RAS genes as well as RET/PTC and PAX8/PPAR? chromosomal rearrangements. Somatic mutations and other molecular alterations have also been recognized as helpful diagnostic and prognostic markers for thyroid cancer.
According to a study based in Balochistan, Quetta has higher incidence rate (up to 1.30) of thyroid cancer than other areas in Balochistan. This can also be because Quetta is the host city of Centre for Nuclear Medicine and Radiotherapy (CENAR), the only cancer facility in Pakistan’s largest province Balochistan. Therefore, there is a huge possibility that other cases of thyroid cancer go undiagnosed. Also, due to lack of awareness and low literacy rate in patients most patients arrive at the last stage of cancer and it’s difficult to save them.
On September 6, 2015, a conference titled National Symposium on “Advancing the Frontiers of Endocrinology in Pakistan” was held in Karachi whose primary focus was endocrine diseases in Pakistan. Experts emphasized that appropriate use of radioactive iodine greatly reduces future risk of thyroid carcinoma without causing any serious symptoms.
In case you are wondering what radioactive iodine is, it is iodine given in a capsule or liquid form and is absorbed by the thyroid gland. The treatment destroys thyroid tissue but does not harm other tissue in the body.
A more thorough population based study and estimation of iodine content in water and food along with study of dietary habits in the community is needed to determine a more accurate picture of the status of thyroid carcinoma in Pakistan. More awareness should be raised to ensure timely diagnosis and treatment of this endocrine disease.
- Bukhari, U., Sadiq, S., Memon, J., & Baig, F. (2009). Thyroid carcinoma in Pakistan: a retrospective review of 998 cases from an academic referral center. Hematology/oncology and stem cell therapy, 2(2), 345-348.
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