Thyroid Cancer – Risk Factors And Symptoms
Thyroid cancer represents a malignant disease in which the cells that form the thyroid gland start to grow abnormal and uncontrollably and form a mass of malignant cells on thyroid gland called tumor. Thyroid gland in an endocrine organ located anteriorly at the base of the throat. The gland usually has a H or a U shape and is formed by two lateral lobes which are connected by a median isthmus. In rare cases, the isthmus may be absent, and the thyroid gland is formed by two distinct lobes.
The thyroid gland is one of the biggest and most important endocrine glands of the body and its activity is regulated by pituitary gland and hypothalamus. It secrets thyroxine, triiodothyronine and calcitonin (a hormone important in calcium homeostasis). The thyroid gland controls metabolic processes, protein synthesis and overall sensitivity of the organism to the action of other hormones.
In United States, thyroid cancers represents 1% of new cancer diagnosis each year, 23.500 cases being diagnosed yearly. The incidence of thyroid cancer is 3 time higher in women than in men and it appears to have an incidence peek around 30 and 40 years old.
Thyroid cancer is classified into papillary carcinomas (represents 80% of all thyroid neoplasms), follicular carcinomas (approximately 10% of all cases), medullary thyroid carcinomas (approximately 5% of all neoplasms), anaplastic carcinomas (1%-2% of all cases), primary thyroid lymphomas and primary thyroid sarcomas, which are very rare.
Thyroid Cancer Risk Factors
Thyroid cancer is quite common, given that in 5% of autopsy are found asymptomatic thyroid malignant lesions. Despite this, death caused by thyroid cancer is uncommon, this is explained by the fact that thyroid cancer is usually a disease that tends to remain localized in the thyroid for many years.
Due to the fact that most thyroid cancers are sporadic, no obvious predisposition or risk factors for developing this disease were found. It is believed that estrogen may represent a risk factor for developing thyroid cancer, because the disease has an increased incidence in women, but recent studies did not demonstrate a link between estrogen and thyroid cancer development.
Epidemiological studies have shown an increased prevalence of certain types of thyroid cancer (follicular and anaplastic carcinomas) in regions with a high incidence of goiter (abnormal enlargement of the thyroid gland) that occurs as a result of a diet low in iodine. This hypothesis is supported by the decreased incidence of thyroid cancer in people who received iodine supplementation.
Radiation exposure significantly increases the risk for thyroid cancer, especially for papillary thyroid carcinoma. In the support of this findings lies the increased incidence of thyroid cancer in children exposed to high dose of radiation after the nuclear bombings in Hiroshima and Nagasaki during world war II and after the nuclear accident in Chernobyl. It was also observed that patients who were treated with low-dose of radiation therapy for benign disease, such as acne or adenotonsillar hypertrophy presented an increased incidence of thyroid cancer. Studies suggest that radiation exposure for imaging studies, radiation therapy for thyroid gland and high-dose radiation beam therapy dose not appear to increase the risk for thyroid cancer. Usually there is a delay of at least several decades between radiation exposure and cancer development.
A genetic predisposition has been associated with medullary thyroid cancer, which may occur as a part of multiple endocrine neoplasia syndrome. Multiple endocrine neoplasia (MEN) syndromes are characterized by simultaneous or sequential combination at the same patient of benign or malignant hyperplastic lesions or tumors, benign or malignant, of at least two endocrine glands without obvious functional interrelations. There are three distinct types of MEN: MEN 1 (Wermer syndrome), MEN 2A syndrome (Sipple syndrome) and MEN 2B syndrome (Shimcke) plus Carney complex. Patients with Sipple syndrome have family history of medullary thyroid cancer and of pheochromocytoma.
Thyroid Cancer Symptoms
In early stages, thyroid cancer does not cause any symptom or may manifests as a solitary, painless and palpable thyroid nodule, which is usually discovered at a routine examination. 4%-7% of general population present palpable nodules and most of them are the result of a benign disease.
The age at which appears a thyroid nodule is very important because in most cases solitary thyroid nodules have a higher risk to be malignant in patients older than 60 years and in patients younger than 30 years. Thyroid nodules in males are more likely to be malignant. A very important sign for malignancy in a painless thyroid nodule is rapid growth in a short period of time.
In first stages of evolution, malignant thyroid nodules are usually painless. Pain with sudden onset is more likely to appear in benign disease such as autoimmune thyroiditis, viral or bacterial thyroiditis or an acute hemorrhage into a benign thyroid cyst.
Physical examination of a malignant thyroid nodule usually reveals a solitary, painless and palpable nodule, which have a consistency that may vary from soft to hard. This nodule is poorly delimited from the surrounding tissues and generally is less mobile with swallowing. An other characteristic for malignancy is represented by the presence of a nontender thyroid mass at palpation which tends to increase rapidly in size. Usually, firm cervical masses suggest rather a limphonodal metastases than a malignant thyroid nodule.
In advanced stages, thyroid cancer causes symptoms by compression of surrounding tissues and organs. Therefore, may occur difficulty or pain when swallowing by compressing the pharynx, difficulties in breathing or shortness of breath by compressing the trachea. In the moment when thyroid cancer is invading the larynx, compressing recurrent laryngeal nerve may appear hoarseness and cough.