Colon Cancer

Colon Cancer

Introduction

Colon cancer, a malignant tumor that develops in the large intestine, accounts for 10% of cancer cases worldwide. Although it is the fourth most common cause of cancer death worldwide and the second most common cause of cancer death in the United States, colon cancer is often preventable with screening and early intervention. Screening and early intervention are also important because they greatly increase the odds o f cure.

The etiology of colon cancer is thought to be multifactorial, with both genetic and environmental factors implicated. The development of colon cancer begins with mucosal cell hyperplasia (i.e., an abnormal increase in the number of cells), which over time forms a benign tumor (e.g., polyp). Dysplasia (i.e., abnormal cell development) then develops and eventually manifests as cancer (e.g., adenocarcinoma), which has the potential to metastasize. The liver is the most frequent site of metastasis. Other common sites of metastasis are the lung, peritoneal cavity, adrenals, ovaries, and bone.

Prognosis is correlated with TNM (tumor, node, metastasis) staging. T (T1-T4) corresponds to the depth of tumor invasion, with T4 being the most invasive. N (N0-N2) describes lymph node involvement. M indicates the presence (M1) or absence (M0) of metastasis. Patients with stage I colon cancer (i.e., T1-2N0M0) have a greater than 90% chance of surviving 5 years, while patients with stage IV disease (i.e., any stage that includes M1) have only an 8% chance of surviving 5 years. Treatment options include surgery (e.g., removal of the primary tumor and/or isolated liver or lung metastases), neoadjuvant chemotherapy (i.e., chemotherapy administered prior to surgery), adjuvant chemotherapy (i.e., chemotherapy administered after surgery), hepatic arterial infusion (HAI; i.e., regional chemotherapy to treat liver metastases), monoclonal antibody therapy (e.g., bevacizumab, cetuximab), and radiation therapy. Treatment follow-up includes clinical and laboratory evaluation every 3-6 months for 5 years, annual imaging studies for 3 years, and colonoscopy at 1 year and then as clinically indicated.

Facts and Figures

The oncology literature often addresses colon and rectal cancer together as colorectal cancer (CRC). In 2008, an estimated 148,810 new cases of CRC were reported and 49,960 patients died of CRC. The incidence of CRC increases with age; more than 90% of patients diagnosed with CRC are older than 50. The anatomy of the rectum and its surrounding structures (e.g., bladder, vagina, prostate, anal sphincter) makes rectal cancer more difficult to treat than colon cancer.

Risk Factors

Screening for colon cancer should begin earlier than age ...