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Colorectal Cancer

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Overview

Colorectal cancer, also known as bowel cancer, occurs in the colon or the rectum-part of the large intestine. The large intestine absorbs water and salts from the undigested material and throws out the waste material. It is composed of the colon, rectum, and anus. Incidentally, colon forms the largest part of the large intestine. Colorectal cancer is the seventh leading cause of cancer death in India. The incidence is lower in India as compared to the western countries. It is eighth most commonly occurring cancer in men whereas ninth most common cancer in women. According to the Globocan 2018 data, there were 19,548 cases of death reported from colorectal cancer.

Types of Colorectal Cancer

Adenocarcinoma

These cancers are the most common form of colorectal cancer. They begin in the glandular cells producing mucus. Mucinous tumors and signet ring tumors are the two rare types of colorectal cancer.

Carcinoid tumors

This type of tumors grows in hormone producing cells in the intestine. These tumors are usually slow growing and also called as neuroendocrine tumor.

Gastrointestinal stromal tumors

Their growth begins in the muscle tissue of the digestive system. They are non-cancerous initially and these rarely appear in the colon.

Sarcomas

Sarcomas in the large intestine are called leiomyosarcomas. These starts in the smooth muscle and are treated in a different manner than adenocarcinomas.

Causes

Lynch syndrome: It is also called as hereditary non-polyposis colon cancer and with mutations in DNA repair genes such as MLH1, MSH2, MSH6, PMS2, and EPCAM leading to the development of cancer.

Familial adenomatous polyposis (FAP), Attenuated FAP (AFAP), and Gardner syndrome: They are caused by inherited mutation in the APC gene which leads to formation of polyps in the colon. Later, cancer may develop in one of these polyps.

MUTYH- associated polyposis (MAP): Mutation in the MUTYH gene, responsible for fixing errors in the DNA while dividing, leads to MAP

Peutz- Jeghers syndrome: It is caused by inherited mutation in the STK11 (LKB1) gene.

Risk Factors

Family history

Increased risk of colorectal cancer if a person from your family is diagnosed with colorectal cancer. If more than one relative is diagnosed with colorectal cancer below 45 years of age then you are at a greater risk of developing it.

Ulcerative colitis & Crohn’s disease

These chronic diseases induce inflammation in the large intestine. The risk of developing colorectal increase if you are suffering from any one of these diseases.

Previous history of colorectal cancer

There are high chances of recurrent colorectal cancer if there is previous history of diagnosis.

Alcohol

Consumption of alcohol is associated with development of colorectal cancer.

Age

The colorectal cancer is most likely to develop in older people than in young people.

Polyps in the colon

Polyps in the colon are non-cancerous but it can develop into cancer over a period of time.

Radiation

Only 2% of the colorectal cancer is linked with radiation exposure.

Signs & symptoms

Some of the symptoms of colorectal cancer are:

Detection of blood in the stool

Diarrhea, constipation, or narrowing of the stool

Bleeding in the rectum

Weight loss, weakness and fatigue

Abdominal pain

Diagnosis

Blood tests

Following blood tests can be done to diagnose colorectal cancer. They are:

  • Complete blood count (CBC): This test will help in determining if a person is anemic. Since, people with colorectal cancer often tend to become anemic.
  • Liver enzymes: Colorectal cancer can spread to the liver. Therefore, blood tests should be performed to check for the liver function.
  • Tumor markers: Elevated levels of Carcinoembronic antigen (CEA) is an important tumor for colorectal cancer.

Colonoscopy

Colonoscope when a person has been diagnosed to have some abnormalities through other screening tests.

Proctoscopy

When there is a suspicious lesion in the rectum, protoscopy is done to see and assess exact location and size.

Biopsy

It is performed during colonoscopy if colorectal cancer has been suspected during any diagnostic test. Certain lab tests are performed for the biopsy samples. These includes gene tests, microsatellite instability (MIS), and mismatch repair genes (MMR) mutation tests.

Imaging tests

Several imaging tests are performed to identify cancerous areas and their spread. These tests include CT scan, ultrasound, MRI scan, chest X-Ray, PET scan, and angiography.

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References