Colorectal cancer (colon cancer)

Colorectal cancer begins when healthy cells in the lining of the colon or rectum change and grow out of control, forming a mass called a tumor. A tumor can be cancerous or benign. A cancerous tumor is malignant, meaning it can grow and spread to other parts of the body. A benign tumor means the tumor can grow but will not spread. These changes usually take years to develop. Both genetic and environmental factors can cause the changes. However, when a person has an uncommon inherited syndrome changes can occur in months or years.

Anatomy of the colon and rectum

The colon and rectum make up the large intestine, which plays an important role in the body's ability to process waste. The colon makes up the first 5 to 6 feet of the large intestine, and the rectum makes up the last 6 inches, ending at the anus.

The colon and rectum have 5 sections. The ascending colon is the portion that extends from a pouch called the cecum. The cecum is the beginning of the large intestine into which the small intestine empties; it’s on the right side of the abdomen. The transverse colon crosses the top of the abdomen. The descending colon takes waste down the left side. Finally, the sigmoid colon at the bottom takes waste a few more inches, down to the rectum. Waste leaves the body through the anus.

Most common type of cancer of the gastrointestinal tract

It is the most common type of cancer of the gastrointestinal tract, and a major cause of death and disease around the world..  The large intestine is found in the abdominal cavity, which can be thought of as having two spaces - the intraperitoneal space and the retroperitoneal space.

Gastrointestinal tract are composed of four layers

The intraperitoneal space contains the first part of the duodenum, all of the small intestines, the transverse colon, sigmoid colon, and the rectum; the retroperitoneal space contains the distal duodenum, ascending colon, descending colon, and anal canal. So the large intestines essentially weave back and forth between the intraperitoneal and retroperitoneal spaces. Now, the walls of the gastrointestinal tract are composed of four layers.

The outermost layer is the called serosa for the intraperitoneal parts, and the adventitia for the retroperitoneal parts.

Next is the muscular layer, which contracts to move food through the bowel. After that is the submucosa, which consists of a dense layer of tissue that contains blood vessels, lymphatics, and nerves. And finally, there’s the inner lining of the intestine called the mucosa; which surrounds the lumen of the gastrointestinal tract, and comes into direct contact with digested food.

The mucosa has invaginations called intestinal glands or colonic crypts, and it’s lined with large cells that are specialized in absorption. Most colorectal carcinomas are adenocarcinomas, meaning that they arise from the cells lining the intestinal glands.

Most cases of colorectal tumors happen because of sporadic mutations, but a small number are caused by known genetic mutations that run in a person’s family. An example of this is the adenomatous polyposis coli gene, or APC gene, which is a tumor suppressor gene.

Normally, the APC protein identifies when a cell is accumulating a lot of mutations and forces it to undergo apoptosis, or programmed cell death.

But when the APC gene is mutated, the mutated bowel cells don’t die, and instead some start dividing uncontrollably, giving rise to polyps. Over time, these polyps might accumulate more mutations in other tumor suppressor genes like the K-ras gene or the p53 gene, and ultimately it might might become a malignant tumor – meaning that the cells might be able to invade neighboring tissues.

Another well known example are genetic mutations in DNA repair genes which help fix up mutations in cellular DNA. When they’re out of action - cells accumulate mutations and over time can develop into polyps and eventually adenocarcinomas.

So, broadly speaking, adenocarcinomas are the malignant evolution of polyps, and polyps arise when cells start dividing faster than usual. There are many different types of polyps, and some are more prone to become malignant; those are called pre-malignant or neoplastic polyps.

These pre-malignant polyps can be classified into adenomatous and serrated, according to how they look under the microscope. Typically, adenomatous polyps have an APC mutation and the cells look like normal colonic mucosa cells, whereas serrated polyps have defects in DNA repair genes and have a saw-tooth appearance.

Stages of Colon Cancer

When tumors become cancerous, they can be categorized into stages.

Stage 0 is carcinoma in situ, meaning that the tumor has not grown beyond the mucosa.

Stage 1 is when the tumor has grown beyond the mucosa, but has not spread to lymph nodes or distant organs.

Stage 2 is when the tumor has invaded the whole colonic or rectal wall, and may have reached nearby organs or tissues, but still hasn’t spread to lymph nodes or distant organs.

Stage 3 is when the tumor had spread to lymph nodes, but still hasn’t spread to distant organs.

Finally, stage 4 is metastatic, meaning that the tumor has spread to distant organs.

The most common site of metastasis for colon cancer is the liver, and for rectal cancer it’s the lungs.

There are some non-modifiable risk factors for colorectal cancer like being an elderly male and having inflammatory bowel disease, but there are some modifiable risk factors as well, like smoking cigarettes, eating a lot of red meat, not eating a lot of fiber, and being obese.

Colorectal cancer are also also associated with specific disorders like familial adenomatous polyposis and hereditary nonpolyposis colorectal cancer. Initially, colorectal carcinoma is often asymptomatic, but as the disease progresses, symptoms can develop depending on the tumor’s location. Tumors in the ascending or right colon generally grow outward beyond the surface of the mucosa, and that can cause vague abdominal pain and weight loss.

Typically, these tumors don’t cause bowel obstruction, which means that they can grow quite large before causing symptoms and that also means that there’s often a late diagnosis. These tumors can ulcerate and bleed, and over time, the bleeding can lead to iron deficiency anemia.

Tumors located on the descending or left colon are generally infiltrating masses, meaning that they tend to be ring-shaped masses that involve the whole circumference of the colonic wall.

This causes lumen narrowing, referred to as napkin-ring constriction, so symptoms of bowel obstruction typically happen early on. Bowel obstruction can cause colicky abdominal pain, and blood-streaked stools, called hematochezia.

source image:Colorectal Cancer Alliance

What is Low Anterior Resection? (LAR)

LAR is a surgery that’s done to treat rectal cancer. During LAR surgery, the part of your rectum with the cancer will be removed. The remaining part of your rectum will be reconnected to your colon. You will be able to have bowel movements (poop) as usual once you recover from your surgery.

Different Technique of LAR Surgery?

When 1 long incision is made on your abdomen, this is called open surgery. The part of your rectum that has the cancer will be removed thorough the incision. When several small incisions are made on your abdomen, this is called minimally invasive surgery. Small surgical tools and a video camera will be put into the incisions to remove the cancer. Some surgeons use a robotic device to assist with the surgery.

Once the part of your rectum with the cancer is removed, the remaining part of your rectum will be reconnected to your colon with tiny metal staples or sutures (stitches). The place where the 2 ends are reconnected is called an anastomosis.

LAR surgery usually takes about 4 hours. 

What are the Symptoms of colon cancer

  • A persistent change in your bowel habits, including diarrhea or constipation or a change in the consistency of your stool
  • Rectal bleeding or blood in your stool
  • Persistent abdominal discomfort, such as cramps, gas or pain
  • A feeling that your bowel doesn't empty completely
  • Weakness or fatigue
  • Unexplained weight loss 

What causes colon cancer 

In general, colon cancer begins when healthy cells in the colon develop changes (mutations) in their DNA. A cell's DNA contains a set of instructions that tell a cell what to do.

Healthy cells grow and divide in an orderly way to keep your body functioning normally. But when a cell's DNA is damaged and becomes cancerous, cells continue to divide — even when new cells aren't needed. As the cells accumulate, they form a tumor.

With time, the cancer cells can grow to invade and destroy normal tissue nearby. And cancerous cells can travel to other parts of the body to form deposits there (metastasis).

What are the Risk factors involved in Colorectal cancer

Factors that may increase your risk of colon cancer include:

  • Older age.Colon cancer can be diagnosed at any age, but a majority of people with colon cancer are older than 50. The rates of colon cancer in people younger than 50 have been increasing, but doctors aren't sure why.
  • African-American race.African-Americans have a greater risk of colon cancer than do people of other races.
  • A personal history of colorectal cancer or polyps.If you've already had colon cancer or noncancerous colon polyps, you have a greater risk of colon cancer in the future.
  • Inflammatory intestinal conditions.Chronic inflammatory diseases of the colon, such as ulcerative colitis and Crohn's disease can increase your risk of colon cancer.
  • Inherited syndromes that increase colon cancer risk.Some gene mutations passed through generations of your family can increase your risk of colon cancer significantly. Only a small percentage of colon cancers are linked to inherited genes. The most common inherited syndromes that increase colon cancer risk are familial adenomatous polyposis (FAP) and Lynch syndrome, which is also known as hereditary nonpolyposis colorectal cancer (HNPCC).
  • Family history of colon cancer.You're more likely to develop colon cancer if you have a blood relative who has had the disease. If more than one family member has colon cancer or rectal cancer, your risk is even greater.
  • Low-fiber, high-fat diet.Colon cancer and rectal cancer may be associated with a typical Western diet, which is low in fiber and high in fat and calories. Research in this area has had mixed results. Some studies have found an increased risk of colon cancer in people who eat diets high in red meat and processed meat.
  • A sedentary lifestyle.People who are inactive are more likely to develop colon cancer. Getting regular physical activity may reduce your risk of colon cancer.
  • People with diabetes or insulin resistance have an increased risk of colon cancer.
  • People who are obese have an increased risk of colon cancer and an increased risk of dying of colon cancer when compared with people considered normal weight.
  • People who smoke may have an increased risk of colon cancer.
  • Heavy use of alcohol increases your risk of colon cancer.
  • Radiation therapy for cancer.Radiation therapy directed at the abdomen to treat previous cancers increases the risk of colon cancer.

How Colon Cancer is Diagnosed

There are several Medical test which can diagnosed the cancer are below mention-

  • Barium Enema
  • Biopsy
  • Colonoscopy
  • Digital Rectal Exam
  • Sigmoidoscopy
  • Endoscopy

Colonoscopy-  which is when a camera is inserted retrograde into the colon and rectum and to take pictures of abnormal looking polyps and a biopsy.

In addition, fecal occult blood testing is often done to look for evidence of gastrointestinal bleeding.

Typically, in colorectal cancer there’s an elevation in the tumor marker CEA, which is a glycoprotein involved in cell adhesion.

However, this is not a very specific finding. A barium enema can be useful as well. That’s where a liquid is injected into the rectum through a small tube, and an X ray is taken to look for abnormalities in the large intestines.

On a barium enema, a classic sign of colorectal cancer is the apple core sign, which shows the constriction of the lumen - most often in the descending colon. To identify colorectal cancer early, routine colonoscopy and fecal occult blood test can be done to look for neoplastic polyps or early carcinomas so that they can be removed at an early stage. This is particularly important for individuals with relatives with colorectal cancer and those with disorders like familial adenomatous polyposis and hereditary nonpolyposis colorectal cancer.

Disease Area: Rectum

Steps:

  • Access through separation of GI layers
  • Identification and mobilization of malignant area
  • Transection, Resection & Anastomosis

Treatment / Surgery for Colon Cancer

Treatment for colorectal cancer depends on the stage of the cancer. Early cancers that are confined to the wall of the colon are often surgically resected, and those that have spread to nearby lymph nodes are often treated with chemotherapy.

Unfortunately, metastatic cancers are typically incurable, but sometimes chemotherapy or surgery can be used to ease symptoms.

colectomy is surgery to remove all or part of the colon. Nearby lymph nodes are also removed. If only part of the colon is removed, it's called a hemicolectomy, partial colectomy, or segmental resection. The surgeon takes out the part of the colon with the cancer and a small segment of normal colon on either side

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