Colon Cancer

Excerpt

Colorectal cancer is the third most common diagnosis and cause of cancer-related death in both sexes in the United States. Worldwide and in the United States, colon and rectal cancers are the second most common cause of cancer-related mortality. Incidence rates have been decreasing in Western countries, mostly due to the widespread use of colonoscopy screening. However, the condition's incidence among younger adults is increasing.

Most colon cancer is sporadic, and approximately 5 percent are due to an inherited genetic mutation, mostly due to Lynch syndrome (hereditary nonpolyposis colon cancer or HNPCC) and familial adenomatous polyposis (FAP). The transition from normal colon epithelium to invasive cancer takes several years and most commonly follows a sequence characterized by the accumulation of genetic mutations, adenoma formation, and subsequent carcinogenesis (adenoma-carcinoma sequence). Certain cancers may follow alternative pathways, such as those involving DNA mismatch repair (MMR) and the BRAF gene.

Colon cancer screening is recommended and may be performed using various modalities. Screening initiation and follow-up guidelines vary among organizations. Colon cancer diagnosis requires a tissue biopsy, usually obtained via colonoscopy. All newly diagnosed colon cancers should be screened for common genetic mutations, and a complete colonoscopy and baseline carcinoembryonic antigen (CEA) should be performed. Most patients with invasive cancer require a baseline chest and abdominopelvic computed tomography (CT) scan.

Surgical resection is the main modality for localized early-stage colon cancer. The most important prognostic indicator is the pathological stage. Staging dictates the need for further therapy, which may include chemotherapy, immunotherapy, or, rarely, radiation. Surveillance after treatment is crucial in detecting metastatic disease and local recurrence, which may be curable with multimodality therapy. Palliative systemic therapy is reserved for nonresectable or widely metastatic disease to improve quality of life and survival.