Colorectal cancer

Colorectal cancers affect the colon or the rectum. 

The colon or the large intestine and the rectum are the parts of your digestive system. These help to absorb water and salts from the food you take in and for removing the waste products after digestion. 

The rectum is, in fact, the last part of the large intestine or colon. If your cancer is limited to the colon, you have colon cancer. If it affects only the rectum, you have rectal cancer. The symptoms are almost the same for both, but the treatments will vary.

Another name for colorectal cancer is bowel cancer. It is the second most common cancer in women and the third common one in men. These cancers are second in terms of deaths due to cancers. 

The exact cause of these cancers is not very clear. Being overweight, smoking, unhealthy diet habits, etc. are some of the risk factors. If you have growths called polyps in the intestine, your risk is more.

Colorectal cancers have very few symptoms in its early stages. Most of the symptoms occur in the later stages. Blood in stools, diarrhea or constipation, changes in bowel habits, etc., are some of them.

Surgery is the most common treatment option for colorectal cancers. If the tumor is large or has spread to other parts of the body, you will need treatments like chemotherapy, radiation as well.

What causes colorectal cancer?

The exact cause of colorectal cancers is not clear.

A healthy cell knows how they should divide or for how long they should live. It is the genes present in the cells that store this knowledge. Any defects or changes in the structure of genes can alter this information. If this happens, the cells may divide at a faster rate and live for longer than usual. The result is cancer. But what is not clear is the reason for the changes in the genes. 

But a few things can increase the risk of getting colorectal cancers.  

Risk factors for colorectal cancers

Risk factors are things that increase your chances of getting cancer. You can avoid some of these while some others are not under your control.

Some of the common risk factors that you can change are

• Your weight- If you are obese or overweight, you are at higher risk.
• Smoking- You are at risk if you smoke. The risk depends on the number of cigarettes you smoke and for how long you have been smoking.
• Too much alcohol- If you are a habitual drinker who drinks beyond the limits, your risk is high
• Lack of exercise- If you lead an inactive life, you are more at risk
• Your food habits- If you eat fewer vegetables and fruits and more meat and processed food, your risk will increase. 

Some risk factors beyond your control are

• Your age- Colorectal cancers are more common in those above the age of sixty. Your risk is more as you age.
• Having colorectal cancer before- If you have a history of the disease, your chance of getting it again is more. 
• Having diseases like type 2 diabetes, ulcerative colitis, Crohn's disease, etc

Interestingly, you may get the disease without any of these risk factors. Also, you may not get it even if you belong to the high-risk group.

Signs and symptoms of colorectal cancer

You will have few symptoms in the early stages of the disease. As the tumor grows in size, you will start having symptoms

Some of these are

• A change in your bowel habits with persistent bouts of constipation or diarrhea
• Presence of blood in the stool
• Bleeding from the rectum or anus
• Difficulty in passing stools
• A feeling that bowel is not empty even after passing stools
• Severe fatigue without a reason
• Sudden loss of weight without trying
• Pain or cramps in the abdomen
• Bowel obstruction may occur as the stage of cancer increases. Severe vomiting may occur as a result.

Diagnosis of colorectal cancer

If you have any of these symptoms, and the doctor suspects cancer, you will have a few tests to confirm or rule it out.

Colonoscopy -It helps the doctor see the inside of the colon or rectum a screen. For, this the doctor will insert a thin and flexible tube through your anus towards the colon. This tube will have a camera at the tip that transmits the images to the screen. If there is cancer, the doctor will know it from the images. It is also possible to do small surgeries during this. For this, the surgeon will push special surgical tips through the tube to the site of cancer. 

Biopsy-  If the doctor suspects cancer, he or she will take a tissue sample for looking under a microscope for cancer cells. It also helps to know about the type and stage of cancer.

MRI and CT scans- These imaging tests will show the spread of cancer to other areas of the body. 

PET scans- You will have it if cancer has spread too far in the body. The test uses a radioactive type of sugar to highlight the areas with cancer and then take images of these areas

Treatments for colorectal cancers

Your colorectal cancer treatment will depend on the stage of the disease. Also, the treatment will vary according to the location of cancer as well. You will have surgery as a first step to remove cancer if it has not spread too much.

But in situations where there is a big tumor in the colon or rectum, you will need other treatments like radiation therapy or chemotherapy. The same applies to cancers that have spread to other areas of the body as well.

Your general health also influences the choice of treatments. Most of the treatments for cancers have some side effects. So you must be healthy enough to withstand these. 

Surgery for colorectal cancer

During surgery, the surgeon will remove the tumor along with a margin of healthy tissue at the borders. It is to make sure that no more cancer remains after treatment.

There are different types of surgeries for colorectal cancers. Some of the common ones are

• Polypectomy- Polyps are small growths that occur in the lining of the colon, which may turn to cancers. During a polypectomy, the surgeon will remove it at its base along with a safe margin of healthy tissue. The surgeon will use a colonoscope, a thin and flexible tube with a camera at the tip. The surgeon will pass this through the anus towards the colon. So there will not be any wound after surgery.
• Endoscopic mucosal resection- You will have this surgery if the cancer is only in the lining of the colon. The surgeon will remove the lining with cancer with the help of a colonoscope.
• Colectomy- It is for cancers that involve a large part of the colon. The surgeon will remove this part by cutting off the tumor at both ends. Then the surgeon will stitch the healthy ends together. The surgery will reduce the length of the colon, making bowel movements faster than usual. 
• Colostomy- At times, the tumor will be so large that it is difficult to remove it by surgery. It may also obstruct bowel movements.In such situations, the surgeon will go for a colostomy. During this, the surgeon will cut the colon before the tumor as a first step. The next step is to create an opening called a stoma in the abdomen. The surgeon will then connect the healthy end of the colon to the stoma. Thus, it creates a path for the movement of waste products of digestion to the outside of the body. There will be a bag that covers the stoma to collect this waste.
• Laparoscopic surgery for colorectal cancers - These surgeries use only two or three small incisions in the abdomen for surgery. The surgeon will insert a camera through one of these to view the surgical site. He or she will then do the surgery by passing special surgical instruments through the other openings. Since the surgical wounds are small, there will be very few complications. The recovery will also be faster.
• Transanal resection- During this surgery, the surgeon will remove the tumor through the anus. It is ideal for small tumors that lie close to the anus. If the tumor is slightly higher up in the rectum, the surgeon may use an endoscope to do the surgery.
• Lower anterior resection-  During this, the surgeon will remove the part of the rectum with the tumor. The surgeon will then connect the colon to the remaining part of the rectum. It helps in the movement of stools through the anus.
• Mesorectal resection-  It is for large tumors that involve the fatty tissue that surrounds the rectum. The surgeon will remove the tumor along with the surrounding fat tissue and lymph nodes. 
• Proctectomy-   During this, the surgeon will remove the whole of the rectum. It is for large tumors of the rectum. The surgeon will then connect the colon directly to the anus.

Chemotherapy- It uses medicines to treat cancers. You will have it as pills or as injections to your veins. You will have the treatment for a few days at a stretch called a 'cycle' with a period of rest in between. It is an ideal treatment for large cancers, where surgery is not an option.

Biologic Therapy - These are directed therapy for certain types of colorectal cancers expressing certain molecular markers ( mutation). These therapies are safer and less toxic and enhance the effect of chemotherapy.

Immunotherapy - Drugs which act of immune system( checkpoint inhibitors) are sometimes used in metastatic cancers, if examination of tumor tissue confirms that this type of therapy will work

Radiation therapy - It uses high energy x-rays or other particles to destroy cancers. The x-rays will be from an external source. The x-rays or particle beams will target the tumor with precision to destroy it. You may have this before surgery to shrink the tumor or after it to destroy any remnants of cancer. In advanced cancers, it helps to provide relief from the symptoms.

The vital factor that affects the outcome of treatments is the stage of the disease. Having treatments in the early will help to improve the success and to prevent the spread of the disease