Rectal Cancer vs. Colon Cancer. What is the difference: Anatomy (Part 1)?

As the term colorectal cancer implies, colon cancer and rectal cancer
are the same, yet different. While the biology of colon cancer and
rectal cancer are the same, the clinical implications of the location
of a cancer are great. This entry discusses the anatomical differences between the colon and the rectum.

Location

The anatomical divisions between the colon and the rectum are two.
Surgeons generally regard the part of the colon that goes beyond the
top of the sacrum bone (the sacral promontory)

Pathologists generally use the "fanning out" of taenia coli as the
beginning of the rectum. Taenia coli are separate longitudinal
ribbons of smooth muscle on the outside of the ascending, transverse,
descending and sigmoid colons. They are visible, and can be seen just
below the serosa. They generally disappear above the level of the
sacral promontory. This anatomic division is important for three
major reasons:
1) The lymphatic drainage of the rectum can change to entirely
different pathway (cancer of the rectum can spread via a different pathway than cancer of the colon)
2) The rectum is closely related to the bones of the pelvis (cancers of the rectum invading into the pelvic bones generally cannot be removed in total with surgery except under some
uncommon circumstances)
3) The rectum is adjacent to the muscular floor of the pelvis and the
nerves which control it, which are responsible for allowing one to
control their bowel movements (removal of cancers of the rectum can radically affect or remove ones ability to control their bowel resulting in fecal incontinence)

Cancers of the colon, even if they invade through the wall of the
colon, rarely invade into bone, or into other structures that cannot
be resected. These cancers predictably spread first to the colon lymph nodes, then to the liver, and then beyond (lungs is the next most common). Resection of the colon usually does not alter ones continence, although the bowel movements may become more loose with extensive colon resection.

Colorectal Cancer at an Early Age

This question was recently posed:

"I was diagnosed with stage IIA colorectal cancer last August, a few months before my 31st birthday...I worry because few people develop this cancer as early as I did. There is no history of cancer in my family. I have been a lacto-ovo vegetarian since I was 18 years old. Do you have any recommendations for how I can prevent recurrence? Could this have been a fluke?"

Differences in Colorectal Cancer in the Young and Old

There is a slight correlation between age at diagnosis and the types of genetic mutations present in colorectal cancer. Cancer in younger people also tends to occur more often on the right side of the colon than the left. We used to think that colorectal cancers in younger people were more aggressive, but this has not proven to be the case. These slight differences don't change the fact that most people diagnosed with colorectal cancer do not have a family history of it and do not have an inherited syndrome associated with it.

Prevention

The problem faced currently is diagnosis of precancerous polyps and cancers in people under the age of 50 who have no family history, because people in this category are not generally being screened with endoscopy. The guidelines for screening put forth by every major organization with an interest in this area do not recommend screening colonoscopy or sigmoidoscopy in this group of patients. For this reason, we rely on this group of patients to be evaluated when they have symptoms that suggest a potential problem such as blood in the stool, unintentional weight loss, loss of appetite, or chronic anemia. Many investigators are working on DNA tests that would help to identify patients at higher risk of colorectal cancer, but these are still early in development.

At the current time, the ways of preventing polyps and colorectal cancer do not differ between young and old patients. Regular surveillance with endoscopy if a patient has a history of colon cancer or polyps is critical. In addition, patients with a history of breast, ovarian, endometrial cancer, or inflammatory bowel disease may be at higher risk for colon cancer and should be screened. All patients with a family history, personal history, or other risk factors for polyps or cancer should discuss with their physician the appropriate tests and intervals for cancer surveillance. In the abscence of risk factors, most organizations recommend initial screening of the colon at age 50.

For chemoprevention, see the previous blog, Chemoprevention and Colorectal Cancer.

Treatment of Stage II Colorectal Cancer

Stage II colorectal cancers are cancers that have developed through the full thickness of the colon wall but have not yet spread to the lymph nodes or any other distant site. This is considered an early stage of cancer and the outcomes from treatment are very favorable. The gold standard of treatment is surgical resection of the tumor. The surgical treatment may be performed as an open procedure or laparoscopically (ie. keyhole surgery). The most important feature of the surgery is that the margins of resection show no evidence of cancer, meaning that the surgeon removed all of the tumor

Preoperative chemoradiation therapy plays a role in some stage II cancers if they are in the rectum. Patients may receive approximately 5 week course of this therapy to shrink the tumor which often increased the success of the surgery that follows. The use of chemotherapy in stage II colon cancer is controversial and is not the standard of care at this point in time so most patients with stage II colon cancer will not receive chemotherapy unless they are enrolled in a clinical trial evaluating the efficacy of chemotherapy.

Most patients with this stage of cancer are cured after undergoing treatment.

Who Should Perform Your Colorectal Cancer Surgery?

Patients with colon & rectal cancer have been shown to have better outcomes when treated by a colon & rectal surgeon. A study in Annals of Surgery, the leading surgical journal in the U.S., demonstrated that specialists in colon & rectal surgery, or surgeons with more extensive experience, had better outcomes for their patients (Ann Surg. 1998 Feb;227(2):157-67).
You can locate a colon & rectal surgery specialist through the American Society of Colon & Rectal Surgeons.

Stoma Problems

Most patients with colorectal cancer requiring a stoma have minimal difficulties with stoma care, however, there are several common problems that can occur and treatment for these problems may range from very simple to requiring surgical revision of the the stoma.

Peristomal Skin Problems

Skin problems associated with a stoma can be caused for a number of reasons. Fungal infections are a common cause of red rash under the stoma appliance and bag because the area is often moist. Often this type of rash will extend down any skin creases. This can be treated using antifungal medications.
Some patients will develop an allergy to the appliance adhesives which causes a reaction only in the area that the adhesive touches. Changing the stomahesive often times cures this.
Poorly fitting stomas can allow leakage from the intestine onto the skin which causes skin irritation which can range from a mild redness to severe ulceration. Leakage can happen for a number of reasons. Sometimes it is because the appliance is cut to the wrong size or an inadequate amount of stoma paste is being used. Other times, anatomical problems with the stoma cause this such as the stoma being located in a skin crease or retraction of the stoma which make pouching difficult.

Stoma Retraction

If the stoma was created under some tension or the patient has gained a lot of weight following surgery, the stoma may retract. This may make pouching the stoma difficult and may require one to use a special wafer which is convex, to conform to the retraction.

Stoma Stricture

Narrowing of the opening of the stoma is called a stricture. This is recognized because the patient may have difficulty evacuating stool from the stoma or even develop intermittent abdominal distension and pain. A stricture may occur from tension on the stoma, poor blood supply to the stoma, or chronic inflammation at the stoma. Treatment may consist of dilating the stoma or may require surgical revision.

Stoma Prolapse

If the stoma begins to get larger such that more of the intestine is protruding away from the abodmen, it is likely that the stoma is prolapsing, meaning that it is telescoping on itself. Prolapse may be managed using an abdominal binder or more likely a surgical revision.

Parastomal Hernia

The stoma is created by making an opening in the abdominal wall for the bowel to pass through. If this opening widens over time, it is possible for other structures such as the small intestine to pass through the abdominal wall along side of the stoma. This is referred to as a parastomal hernia. This may produce a bulge around the stoma making the appliance fit poorly. It may also cause abdominal pain, symptoms of bowel obstruction, or it may be without symptoms. Parastomal hernias which are symptomatic should usually be repaired surgically.

The Risk Factors of Colon & Rectal Cancer

Alcohol

In 1984 a large trial published in the New England Journal of Medicine demonstrated a 3-fold increase in risk of colorectal in men whose usual monthly consumption of beer was 500 oz (15 liters) or more.

Smoking

A large Veterans Administration trial published last year (JAMA. 2003 Dec 10;290(22):2959-67) demonstrated a nearly 2-fold increase in colon cancer risk in patients who were actively smoking.

Obesity

In 1995, the Harvard Medical School Department of Public Health published a trial that studied over 47000 people and their risk factors for colon cancer. Patients with a high hip-to-waist ratio, a measure of obesity, had more than a 3-fold increase in colon cancer risk. Those with a waist size greater than 42 inches had a 2-fold increase risk of cancer. In addition, physical activity was found to reduce the risk of cancer by half.

Diabetes

Studies presented at the 2004 Digestive Disease Week meeting demonstrated that people with diabetes have a 32% increase risk of colon cancer when compared to non-diabetics. This adds to information presented in the journal Gastroenterology in October 2004 which demonstrated that the use of insulin was associated with increased risk of colon cancer and that the duration of using insulin was important in determining risk. Patients receiving insulin for 3 years had a 3-fold increased risk of colon cancer.

Staging Colon Cancer

After colon cancer has been diagnosed, tests are done to find out if cancer cells have spread within the colon or to other parts of the body. The process used to find out if cancer has spread within the colon or to other parts of the body is called staging. The information gathered from the staging process determines the stage of the disease. It is important to know the stage in order to plan treatment.

The following tests and procedures may be used in the staging process:

CAT scan:

A procedure that makes a series of detailed pictures of areas inside the body, taken from different angles. The pictures are made by a computer linked to an x-ray machine. A dye may be injected into a vein or swallowed to help the organs show up more clearly. This procedure is also called computed tomography, computerized tomography, or computerized axial tomography.

Lymph node biopsy:

The removal of all or part of a lymph node. A pathologist views the tissue under a microscope to look for cancer cells

Complete blood count:

A procedure in which a sample of blood is drawn and checked for the following:

• white blood cells
• platelets
• hemoglobin

Carcinoembryonic antigen (CEA) assay:

A test that measures the level of CEA in the blood. CEA is released into the bloodstream from both cancer cells and normal cells. When found in higher than normal amounts, it can be a sign of colon cancer or other conditions.

MRI (magnetic resonance imaging):

A procedure that uses a magnet, radio waves, and a computer to make a series of detailed pictures of areas inside the body. This procedure is also called nuclear magnetic resonance imaging (NMRI).

Chest x-ray:

An x-ray of the organs and bones inside the chest. An x-ray is a type of energy beam that can go through the body and onto film, making a picture of areas inside the bone.

Surgery:

A procedure to remove the tumor and see how far it has spread through the colon.

The following stages are used for colon cancer:

Stage 0 (Carcinoma in Situ)

In stage 0, the cancer is found in the innermost lining of the colon only. Stage 0 cancer is also called carcinoma in situ.

Stage I

In stage I, the cancer has spread beyond the innermost tissue layer of the colon wall to the middle layers. Stage I colon cancer is sometimes called Dukes’ A colon cancer.

Stage II

Stage II colon cancer is divided into stage IIA and stage IIB.

• Stage IIA: Cancer has spread beyond the middle tissue layers of the colon wall or has spread to nearby tissues around the colon or rectum.
• Stage IIB: Cancer has spread beyond the colon wall into nearby organs and/or through the peritoneum.

Stage II colon cancer is sometimes called Dukes' B colon cancer.

Stage III

Stage III colon cancer is divided into stage IIIA, stage IIIB, and stage IIIC.

• Stage IIIA: Cancer has spread from the innermost tissue layer of the colon wall to the middle layers and has spread to as many as 3 lymph nodes.

• Stage IIIB: Cancer has spread to as many as 3 nearby lymph nodes and has spread:

• beyond the middle tissue layers of the colon wall; or
• to nearby tissues around the colon or rectum; or
• beyond the colon wall into nearby organs and/or through the peritoneum.

• Stage IIIC: Cancer has spread to 4 or more nearby lymph nodes and has spread:

to or beyond the middle tissue layers of the colon wall; or

to nearby tissues around the colon or rectum; or

to nearby organs and/or through the peritoneum.

Stage III colon cancer is sometimes called Dukes' C colon cancer.

Stage IV

In stage IV, cancer may have spread to nearby lymph nodes and has spread to other parts of the body, such as the liver or lungs. Stage IV colon cancer is sometimes called Dukes’ D colon cancer.