**1. Introduction: colorectal cancer (CRC)**

There are over a million new cases of colorectal cancer (CRC) being diagnosed worldwide each year [1]. CRC is known to be the third most commonly diagnosed cancer malignancy worldwide and is the fourth most frequent cause of cancer related cell deaths, with around 0.6 million deaths annually [2].

CRC is an uncontrolled growth that originates within polyps that are found in the inner lining of either the colon or rectum [3]. The intestinal wall of the colon and rectum is made up of many layers [3]. CRC polyp growth formation begins within the innermost mucosal layers of either the colon or rectum and these polyps can grow outward through some or all of these intestinal layers [1]. When CRC primary polyp cells growth spreads from the inner to the outer intestinal walls, they can grow into

blood or lymph vessels and so spread to other parts of the body forming secondary cancer metastasizes [1]. Adenocarcinomas polyps originate within intestinal cells that produce mucus to lubricate the inside of either the colon or rectum and this is the most common form of CRC, with approximately 96% of cases, being diagnosed annually [3]. Other less common types of CRC tumors that can originate in colorectal tissues or cells include: lymphomas, sarcomas, gastrointestinal carcinoid or stromal tumors [3].

The risk of developing of CRC is often attributed to either a variety of environmental factors or genetic predispositions. Approximately 25% of diagnosed CRC cases can be attributed to inherited syndromes, while the remaining 75% cases are due to external environmental contributing factors [4, 5]. The most common CRC inherited syndromes include familial adenomatous polyposis (FAP) and hereditary nonpolyposis colorectal cancers (HNPCC) [4]. While common triggering environmental factors include: diets which are low in fiber and high in fat and red meat, low physical activity, obesity, heavy alcohol consumption, cigarette smoking and deskbound seated occupations [5].

Even though numerous advances have been made in relation to early diagnosis and treatment of CRC, tumor reoccurrence and metastatic spread are two critical factors which affect the survival rate of patients [6]. Dependent on the stage at which they have been diagnosed, approximately 25% of patients with CRC at time of diagnosis have metastases (due to late detection) and 50% of patients diagnosed with CRC will develop metastases, either at presentation or during follow-up [7, 8].
