Chapter 16 - Rectal cancer

Abstract

Colon and rectal cancer (CRC) affect approximately 1 million individuals worldwide annually. In Western countries, disease-specific mortality has been declining by 1.6%–2% per year on account of screening programs. However, the incidence of colorectal cancer in individuals under 50 years of age has been increasing by 2.1% per year. Males and females are affected equally. Most colorectal cancer is sporadic and is derived from adenomas. Chronic inflammatory bowel disease (ulcerative colitis, Crohn’s disease) increases the risk for developing CRC. Adenomatous polyps form in the colon when normal mechanisms regulating epithelial renewal are disrupted. This is known as the adenoma-carcinoma sequence. Mutations of several oncogenes and tumor-suppressor genes are involved in this sequence. Rectal cancer is frequently symptomatic and may present with blood per rectum, a change in bowel habits, tenesmus, and rarely rectal pain. A digital rectal examination may reveal a palpable mass. In addition, it may obtain important information such as size, lesion circumference relative to the lumen, whether the lesion is anterior or posterior, fixed, or mobile, its relationship to the sphincter mechanism, and sphincter function. Pretreatment assessment is usually performed to clinically “stage” rectal cancer. The most common modalities used are endorectal ultrasound, MRI of the abdomen and pelvis and CT scan of the chest abdomen and pelvis. This assessment is fundamental in planning for rectal cancer treatment. The surgical standard of care for rectal cancer is total mesorectal excision (TME). An anastomosis may be constructed if appropriate surgical and oncological principles are followed. An abdominoperineal operation is performed when a sphincter-saving procedure is not possible. Clinical stage I patients proceed directly to surgery. Clinical stage II, III patients usually undergo neoadjuvant chemoradiotherapy. Local excision of rectal cancer may be a treatment option in highly selective cases.