Colorectal cancer (CRC) develops in the colon or the rectum, also known as the large intestine.  Colorectal cancers have different characteristics based on their location within the colon or rectum.  For example, tumors in the proximal (right) colon are more common among women and older patients, whereas distal (left) tumors are more common among men and younger patients.  It usually takes about 10 to 20 years for CRC to develop. Most begin as a polyp, also known as a non-cancerous growth, which develops on the inner lining of the colon or rectum.  An adenoma is the most common kind of polyp, which arises from glandular cells.  Adenomas have the ability to become malignant, however more than 90% do not progress to invasive cancer.  Cancer that develops in glandular cells is called adenocarcinoma, which comprises approximately 96% of all colorectal cancers.

Colorectal Cancer Statistics 

Colorectal cancer (CRC) is the third most commonly diagnosed cancer and the third leading cause of cancer death in both men and women in the United States.  Although the incidence and mortality from colon cancer have been on a slow decline over the past two decades, an estimated 93,090 individuals will be diagnosed with colon cancer in the US in 2015, and combined estimates for colon and rectal cancer are 49,700 deaths in 2015.  Worldwide, CRC is the second most common cancer in women and the third most common in men. The incidence of CRC is relatively equal between men and women.

What causes Colorectal Cancer? 

Colorectal cancer is a multifactorial disease process, and both non-modifiable and modifiable risk factors can play a role in the development of CRC.  Current research indicates that genetic factors and family history have the greatest correlation to colorectal cancer.  The progression from an adenoma (premalignant lesion) to an invasive adenocarcinoma is often associated with genetic alterations. Those with a first-degree relative (parent, sibling, or offspring) who have had CRC have 2 to 3 times the risk of developing the disease compared to those with no family history.  About 5% of patients with CRC have a well-defined genetic syndrome.  The most common of these is Lynch Syndrome (also known as hereditary nonpolyposis colorectal cancer).  Lynch Syndrome is part of a subset of genetic diseases that causes colorectal cancer due to deficient DNA mismatch repair.  Lifetime risks of CRC development in individuals with Lynch Syndrome is approximately 66% in men and 43% in women.  Familial adenomatous polyposis (FAP) is the second most common genetic syndrome that predisposes an individual to CRC.  FAP is caused by the hereditary mutation of the APC gene (adenomatous polyposis gene).  The lifetime risk of developing CRC in a person with FAP approaches 100% by age 40.  Additionally, individuals who suffer from inflammatory bowel disease, such as ulcerative colitis and Crohn’s disease, have a higher risk of developing colorectal cancer.  Modifiable risk factors include sedentary lifestyle, obesity, high consumption of red and/or processed meats, tobacco smoking, and alcohol consumption.

What are early symptoms of Colorectal Cancer? 

Due to the strong emphasis on screening procedures, CRC is often detected before any signs or symptoms occur.  In other cases, however, signs can be very nonspecific, such as fatigue, cramping, constipation or weight loss.  In more advanced cases, there can be abdominal tenderness or rectal bleeding.  The clinical presentation can sometimes be dictated by the location of the tumor.  Proximal, or right-sided, tumors can cause diarrhea and are more likely to bleed, which may result in iron-deficiency anemia.  Distal, or left-sided, lesions are more often discovered later in the disease progression, and may present as a bowel obstruction.

How does my doctor know I have Colorectal Cancer? 

Screening plays an important role in the diagnosis of both precancerous and cancerous lesions.  Screening includes colonoscopy every 10 years, beginning at age 50 in asymptomatic men and women.  Other screening tests include flexible sigmoidoscopy (every 5 years), barium enema (every 5 years), and CT colonography (every 5 years). Screening should start at an earlier age and occur more frequently for individuals who are at a higher risk of developing colorectal cancer, such as those with prior history of polyps, prior or family history of colorectal cancer, or history of inflammatory bowel disease.  Any suspicion of colorectal cancer warrants a rectal examination and colonoscopy with biopsy of any questionable lesion.  Tissue biopsy is the gold standard of diagnosis. Other laboratory studies are done to assess patients’ organ function, as well as imaging of chest and abdomen to help determine tumor staging.

What does Classification and Staging of my Colorectal Cancer mean? 

The stage describes the growth and extent to which the cancer has spread at the time of diagnosis.  The staging is crucial in deciding which treatment regimen to consider and plays a major role in prognosis.  The two most common staging systems are the Surveillance, Epidemiology, and End Results (SEER) summary staging system and the TNM system.  The SEER summary staging system is described below:

The TNM staging system is most commonly used in clinical settings. The “T” stands for the primary tumor size, the “N” for whether the cancer has spread to lymph nodes, and the “M” for whether the cancer has spread to other parts of the body (metastasis).  The T, N, and M are then combined to form the stage of the cancer (from stage 0 to stage IV).

Stage 0 is carcinoma in situ. At this stage, the polyp is removed via surgical resection (polypectomy) or local excision through a colonoscope.  Some cases require resection of a segment of the colon if the tumor is too large to be removed by local excision alone.

Stage I and II are early stage, localized tumors. In these two stages, the tumor has penetrated through at least one layer of the colon or rectal wall. Some cancers in stage II may have grown to adjacent organs or structures.  The tumor, a length of colon on either side of the tumor, and nearby lymph nodes are all surgically resected as the standard treatment.

Stage III includes cancers that have spread to multiple nearby lymph nodes.  In this case, surgical resection of the segment of colon containing the tumor is the primary treatment, usually followed by chemotherapy.  If the cancer has grown into adjacent tissues, radiation therapy may be recommended.

Stage IV (metastatic) colorectal cancer has spread to distant organs and tissues.  Surgery is not recommended for all patients, and is usually only performed in order to relieve or prevent blockage of the colon, or to prevent other local complications.  Chemotherapy, radiation, and immunotherapies may be given alone or in combination at this stage.