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General Overview

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Colorectal cancer (CRC) accounts for the third most common type of cancer and third leading cause of cancer mortality in the United States for both men and women.1 As with most cancers, CRC is more likely to have better survival outcomes the earlier it is diagnosed. Colon cancer and rectal cancer are usually grouped together in epidemiological studies and share similar pathophysiology, but there are distinct approaches to treatment. Conventional therapies including surgery, radiation, and chemotherapy are still typically used today depending on the stage and type of cancer. Newer therapies are increasingly used that target specific pathways of the cancer's biology.

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Pathophysiology

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Most CRCs are believed to be a result of an accumulation of genetic mutations that transforms normal epithelial cells into nonmalignant adenomas or polyps, then finally malignant adenocarcinomas. Mutations can originate due to hereditary syndromes or be acquired through lifestyle or environmental risk factors.2

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Key Definitions
  • Adenocarcinoma—malignant neoplasm of epithelial cells with glandular or glandlike features.
  • Adjuvant—in oncology, treatment added after primary therapy, usually a surgery, with the goal to reduce recurrence.
  • CEA—carcinoembryonic antigen, tumor marker found in the serum for colorectal cancer but is also elevated in other malignant and nonmalignant conditions such as smoking.
  • Chemoradiation—chemotherapy given concomitantly with radiation, usually with radiosensitizing agents like fluoropyrimidines or platinums.
  • Microsatellite instability—when microsatellites, repeated sequences of DNA that are usually of a set length, accumulate errors and become longer or shorter than normal.
  • Neoadjuvant—in oncology, treatment added before primary therapy, usually a surgery, with the goal to improve outcomes of that curative therapy.
  • TNM staging—method of classifying cancers by T: tumor size, N: lymph node involvement, and M: presence of distant metastases; the combination of these three factors categorizes a cancer into "stages"; the higher the stage number the more widespread the cancer and generally the worse the prognosis.
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Epidemiology

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CRC is the third most common cancer in both men and women in the United States, making up an estimated 10% of all cancers in 2009 and total 9% of all cancer deaths. Despite these staggering statistics, death rates from CRC have been declining in the past few decades, with an approximate 30% decrease since 1990. Five-year relative survival rates of persons diagnosed with CRC have been significantly increasing over the past 30 years and are most recently estimated at 65% in 2004.1

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Clinical Presentation/Signs and Symptoms

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The clinical presentation of CRCs can be nonspecific which can result in the delay of a diagnosis. Gastrointestinal bleeding, abdominal pain, and change in bowel habits (constipation, abnormal stools) are common at presentation if the patient is symptomatic. Patients sometimes experience significant weight loss, and a partial or complete bowel obstruction may trigger a diagnosis. The pattern of ...

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