Thyroid Cancer

INTRODUCTION

Thyroid cancer is a relatively rare tumor but it is the most common endocrine malignancy worldwide and has increasingly become a public health problem over the past two decades [1]. In recent years, the incidence of thyroid cancer has increased at an alarming rate, especially in developed countries. Thyroid cancer is the tenth most common cancer in Canada [2]. Furthermore, the incidence rate of thyroid cancer is increasing more rapidly than any other cancer in Canada [3, 4]. Typically, most forms of thyroid cancer (TC) have been treated through surgery, conventional radiotherapy and chemotherapy. However, these therapies fail to treat the most invasive forms of this cancer. Recent discoveries of the genetic and molecular pathways involved in TC have uncovered possible new therapeutic targets.

The thyroid is an endocrine gland located at the front of the neck, above the central trachea and below the larynx. Within the hypothalamic-pituitary-thyroid axis, thyrotrophin-releasing hormone (TRH) stimulates the secretion of thyroid stimulating hormone (TSH) from the anterior pituitary [5]. TSH then acts on thyroid gland which releases the iodine dependent hormone thyroxine (T4) and triiodothyroxine (T3) to control physiological functions such as metabolism, heart rate, blood pressure, and body temperature [5].

Etiology

There are several risk factors for TC including patient history, family history, genetic factors, age, gender, and environmental factors such as ionizing radiation exposure and iodine deficiency [5, 6]. During the first 20 years of a person’s life, exposures to ionizing radiations can be particularly damaging to the thyroid gland. These radiations generate free water or oxygen radicals which directly...

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... the initial drug effects wane down over time as alternate pathways compensate. Overcoming these mechanisms of resistance to KI is the next step to prolong the effects of targeted therapies. Fortunately, understanding of epigenetic mechanisms such as histone modifications or RNAis has been greatly advanced in recent years and there is hope that they can be employed in treating thyroid cancers.

These advances have been accompanied by challenges in clinical trials. Besides the fact that clinical samples sizes are usually very small, experimental biomarkers and clinical end points have been controversial in studying thyroid cancers. Better understanding of different mechanisms helped researchers achieve a step forward in managing thyroid cancers. It remains positive to be seen whether new therapeutic combinations could increase long-term survival for thyroid cancers.