Cáncer de colon

The colon and rectum are parts of the body’s digestive system and together form a long, muscular tube called the large intestine. The colon is the first 6 feet of the large intestine and the rectum is the last 8-10 inches. Treatment approaches differ between cancers of the colon or rectum and are, therefore, discussed separately. A separate section has been created for Rectal Cancer.

Adenocarcinoma refers to cancer that begins in the cells that line the colon or large intestine and accounts for over 90%-95% of cancers originating in the colon. Other cancers, including carcinoid tumors and leiomyosarcoma, also originate in the colon, but are not referred to as colon cancer. This treatment overview deals only with adenocarcinoma of the colon, which will be referred to as colon cancer.

The treatment of colon cancer typically consists of surgery and/or chemotherapy and may involve several physicians, including a gastroenterologist, a surgeon, a medical oncologist and other specialists. Care must be carefully coordinated between the various treating physicians involved in managing the cancer.

Colon cancer begins in cells that line the colon. As the cells increase in number, they spread circumferentially around the colon like a “napkin ring.” If detected early, cancer cells may only be found in the colon. If not detected early, the cancer may invade adjacent organs and spread through the lymph and blood systems throughout the body to the liver, lungs and other organs.

After colon cancer has been diagnosed, tests will be performed to determine the extent and characteristics of the cancer. Based on these tests, treatment of colon cancer is personalized for each individual.

STAGING

Determining the stage of the cancer or the extent of the spread requires a number of tests and is ultimately confirmed by surgical removal of the cancer and exploration of the abdominal cavity. The following tests may be used to look for cancer in the chest, abdomen and pelvis.

Computed Tomography (CT) Scan: A CT scan is a technique for imaging body tissues and organs, during which X-ray transmissions are converted to detailed images, using a computer to synthesize X-ray data. A CT scan is conducted with a large machine positioned outside the body that can rotate to capture detailed images of the organs and tissues inside the body. This method is more sensitive and precise than an X-ray.

Magnetic Resonance Imaging (MRI): MRI uses a magnetic field rather than X-rays, and can often distinguish more accurately between healthy and diseased tissue. MRI gives better pictures of tumors located near bone than CT, does not use radiation as CT does, and provides pictures from various angles that enable doctors to construct a three-dimensional image of the tumor.

Colonoscopy: Because 3-5% of patients with a colon cancer can already have an additional cancer in their colon, colonoscopy is routinely recommended to identify whether a second cancer is present in the colon prior to surgery. During a colonoscopy, a long flexible tube that is attached to a camera is inserted through the rectum, allowing physicians to examine the internal lining of the colon for polyps or other abnormalities. Patients are given medication to minimize discomfort. The physician may perform a biopsy in order to collect samples of suspicious tissues or cells for closer examination.

Ultrasound: Ultrasound is a technique that uses sound waves to differentiate tissues based on varying tissue density. Ultrasound can be used transdermally (through the skin), transrectally (using a small probe inserted into the rectum) or intraoperatively (during surgery or during colonoscopy, which is called endoscopic ultrasound).  Transrectal or endoscopic ultrasound may be used in conjunction with CT or MRI scans to help with staging.

SURGERY

Upon completion of the clinical staging evaluation, surgery is performed to remove the cancer along with part of the normal adjacent colon and determine the level of spread within the colon and abdomen. Surgery is performed through an abdominal incision or through a laparoscope. Laparoscopic surgery is less invasive and involves the insertion of surgical instruments through very small incisions in the abdomen. Patients experience faster healing times compared with traditional abdominal surgery, and their outcomes with regard to cancer recurrence and survival have been shown in some trials to be similar.(1) It is important for patients to discuss the risks and benefits of the two techniques with their doctor, as laparoscopic surgery is not yet the standard of care, but is still considered investigational.

Following surgical removal of colon cancer and examination of removed tissue under a microscope, a final “pathologic” stage will be given.

ONCOTYPE DX

A newer test that may help guide treatment decisions for patients with Stage II colon cancer is the Oncotype DXcolon cancer test. This test—which is similar to a test that is commonly used for patients with early-stage breast cancer—is performed after surgery but before final decisions are made about adjuvant (post-surgery) therapy. The test estimates the risk of cancer recurrence by evaluating the activity of certain genes in a sample of tumor tissue.(2) Risk of recurrence can vary greatly among patients with Stage II colon cancer, and use of the Oncotype DX test in combination with other markers of risk may help to individualize treatment decisions. Adjuvant (post-surgery) chemotherapy is not routinely recommended for all patients with Stage II colon cancer, but may be considered for high-risk patients.

KRAS Testing

For patients with metastatic colon cancer (cancer that has spread to distant sites in the body), a sample of the cancer may be tested for mutations in the KRAS gene.(2) Cancers that contain KRAS mutations are unlikely to respond to two targeted therapies that may be used in the treatment of metastatic colorectal cancer: Erbitux®(cetuximab)(3) and Vectibix® (panitumumab).(4)

All treatment information concerning colon cancer is categorized and discussed by the stage. In order to learn more about the most recent information available concerning the treatment of colon cancer, click on the appropriate stage.

Stage I: Cancer is confined to the lining of the colon.

Stage II: Cancer may penetrate the wall of the colon into the abdominal cavity or other adjacent organs but does not invade any local lymph nodes.

Stage III: Cancer invades one or more of the local lymph nodes but has not spread to other distant organs.

Stage IV: Cancer has spread to distant locations in the body, which may include the liver, lungs, bones or other sites.

Recurrent/Relapsed: Colon cancer has progressed or returned (recurred/relapsed) following initial treatment.

References

1. Kuhry E, Schwenk WF, Gaupset R, Romild U, Bonjer HJ. Kuhry E, Schwenk WF, Gaupset R, Romild U, Bonjer HJ. Cochrane Long-term results of laparoscopic colorectal cancer resection. Cochrane Database of Systematic Reviews2008;2:CD003432. Cochrane Database of Systematic Reviews 2008;2:CD003432.

2. National Comprehensive Cancer Network. NCCN Clinical Practice Guidelines in Oncology.™ Colon Cancer. V.3.2008. © National Comprehensive Cancer Network, Inc. 2008. NCCN® and NATIONAL COMPREHENSIVE CANCER NETWORK® are registered trademarks of National Comprehensive Cancer Network, Inc.

3. Karapetis CS, Khambata-Ford S, Jonker DJ et al. K-ras mutations and benefit from cetuximab in advanced colorectal cancer. New England Journal of Medicine. 2008;359:1757-65.

4. Amado RG, Wolf M, Peeters M et al. Wild-type KRAS is required for panitumumab efficacy in patients with metastatic colorectal cancer. Journal of Clinical Oncology. 2008;26:1626-1634.

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