What is Colon Cancer?
Colon cancer, also known as bowel cancer or colorectal cancer or cancer of the bowel, is the cancer of large intestine (lower part of the digestive system). Majority of colon cancer cases start as small and non-cancerous clumps of the cells known as adenomatous. After a certain period of time, these polyps become colon cancers.
Types of Colon Cancer
Adenocarcinoma is considered as the most common type of colon cancer. This type of colon cancer begins in the inner layer that spreads deep into the other layers. Adenocarcinoma can be further categorized into two subtypes that include –
- Signet Ring Cell Adenocarcinoma
- Mucinous Adenocarcinoma
Other Types of Colon Cancer
Gastrointestinal Stromal Tumors : This is considered as a rare type of colon cancer that begins in a cell found in the gastrointestinal tract lining known as interstitial cells of Cajal (ICCs). These type of tumors are classified as sarcomas that include cartilage, fat, bones, blood vessels, deep skin tissues, muscle and nerves.
Squamous Cell Carcinomas: Certain portions of the gastrointestinal tract such as the end of the anus and the upper part of the esophagus are lined with squamous cells. Squamous cell carcinomas are those cancers that begin in these cells.
Leiomyosarcomas: This type of cancer typically means- cancer of smooth muscle. This is considered as a rare type that account for only 0.1% of all colon cancer cases.
Gastrointestinal Carcinoid Tumors: This type of colon cancer is considered as a slow-growing cancer that develops in the neuroendocrine cell in the GI tract lining.
Melanomas: This type is primarily related with skin but can also happen anywhere that include recturm or colon.
Primary Colorectal Lymphomas: The cancers that grow in the lymphatic system of cells (lymphocytes) are known as lymphomas. Primary colorectal lymphomas develop in the later stages of life and are more commonly seen in men as compared to women.
Causes of Colon Cancer
The uncontrollable growth of cells that do not die causes cancer. There is a normal cycle of growth, division and death in case of normal cells but colon cancer do not experiences this type of normal cycle and continue to grow and divide. There are no as such known causes of colon cancer.
Symptoms of Colon Cancer
The early symptoms of colon cancer include –
- Unexplained weight loss
- Bleeding from the rectum or blood in the stools
- Abdominal pain
- Change in normal bowel habits that continue for more than 3 weeks including passing of stools more frequently, diarrhea or constipation
Sometimes bleeding happens when the colon cancer progresses. Gradually, there will be not enough red blood cells in the body that is called as anemia. Following are some of the symptoms of anemia –
- Breathlessness
- Fatigue
Also obstruction is caused by the colon cancer that include following symptoms –
- Vomiting
- A feeling of bloating, especially near the belly button
- Constipation
- Abdominal pain
Stages of Colon Cancer
Stage 1: In the first stage, cancer has not spread further than the original tumor.
Stage 2: The second stage is marked by the growth of tumors through the bowel wall that are close to the tissues. However, this growth has not spread to any part of the body.
Stage 3: In the third stage, there are tumor cells close to the lymph nodes.
Stage 4: The last stage is marked by the spread of the tumor to other parts of the body.
Diagnosis of Colon Cancer
A number of tests are performed for diagnosing colon cancer that include –
- Carcinoembryonic Antigen (CEA) Assay : CEA levels in the blood are measured in this test. The normal as well as cancer cells release CEA in the bloodstream. When these CEA is found in large amounts then it indicates colon cancer.
- Proctoscopy: A proctoscope (a thin and tube-like instrument having light and lens for viewing) is inserted into the rectum in this rectum test. Sometimes removal of the tissue is also done by using a tool in order to check the presence of a disease by examining under a microscope.
- Physical Examination and History: This is done for examining the general signs of health and also for seeing any indications of disease that may include lumps. Proper evaluation of the history of a patient is done that include past illnesses and treatments taken.
- Colonoscopy: This test is performed for viewing the colon and rectum from within in order to see the presence of cancer, polyps or abnormal areas.
- Digital Rectal Exam (DRE): This is considered as a test of the rectum. The insertion of the gloved and lubricated finger is done into the lower part of the rectum for viewing the presence of lumps. Vagina is examined in case of women.
- Biopsy: The signs of cancer are checked by removing tissues or cells that are then examined under a microscope. The removal of tissue at the time of biopsy is helpful in checking the gene mutation in a patient that is responsible for causing HNPCC. The other two tests include –
- Immunohistochemistry Study : Certain antigens are checked by using some substances such as radioisotope, dye or an antibody and they are then added to a tissue sample.
- Reverse-Transcription Polymerase Chain Reaction (RT-PCR) Test : Function of genes or the changes in the structure in a tissue sample are examined by using certain types of chemicals.
Certain other tests are also required for finding the cancer cells that have spread inside the rectum and colon or possibly to other body parts that include –
- Carcinoembryonic Antigen (CEA) Assay
- Chest x-ray
- Positron Emission Tomography Scan (PET)
- CT scan
- Endoscopic Ultrasound (EUS)
- Magnetic Resonance Imaging (MRI)
Treatment of Colon Cancer
There are six treatment options for colon cancer that include –
Targeted Therapy : Certain substances and drugs are used by the targeted therapy in order to target particular cancer cells without causing any harm to nearby normal cells. The two types of targeted therapy include –
- Angiogenesis Inhibitors: This helps in stopping the growth of new blood vessels which tumors need to grow.
- Monoclonal Antibodies: These antibodies are prepared in the laboratory with the help of a single type of immune system. Certain substances can be identified by these antibodies that are on the cancer cells or it also indentifies certain normal substances that are helping in the growth of cancer cells. These antibodies then attach themselves with the substances for destroying cancer cells and also prevent them from spreading.
Chemotherapy: Certain types of drugs are used for stopping the growth of cancer cells or for destroying the cancer cells. The injection of these drugs is done into a vein from where they enter the bloodstream and they then travel through the entire body.
Radiation Therapy: High-energy beams are used for destroying cancer cells. Internal radiation and external radiation are the two types of radiation therapy. A radioactive substance that is sealed in catheters, needles wires or seeds is placed close to the cancer in the case of internal radiation. On the other hand, linear accelerators outside the body are used for sending radiation to the cancer in the case of external radiation. The type of radiation depends on the stage and type of the cancer.
Surgery: The surgical procedure involves the removal of diseased segment with sufficient margins, surrounding lymph nodes and tissue. Following are some of the types of surgeries performed –
- Pelvic Exenteration: The removal of lower rectum, bladder and colon are done when the cancer has spread to different organs nearby the rectum. In the case of women, nearby lymph nodes, vagina, ovaries and cervix are removed. The prostate is removed in the case of men. For flowing the urine and stool out of the body, artificial openings are made in order to collect them in a bag.
- Polypectomy: During a colonoscopy, a polyp is removed if the cancer is found inside a polyp.
- Resection: The removal of nearby healthy tissue and a section of the rectum having cancer is done when the cancer has spread to the wall of the rectum.
- Local Excision: A small amount of nearby healthy tissue and the cancer is removed when the cancer has spread to the inside surface of the rectum and also has not spread into the rectum wall.
Sometimes chemotherapy or radiation therapy is provided after surgery in order to shrink the tumor. This makes the removal of the tumor easy while simultaneously lessening the problems associated with bowel control after surgery. Neoadjuvant therapy is the name given to the treatment that is given before the surgery.