Colorectal

Colorectal Cancer Facts

What is colorectal cancer?

Colorectal cancer is the 3rd most common cancer in men and women. It currently affects 1 in 22 men and 1 in 24 women.

We describe cancer and what causes it in general in another article. When this type of abnormal growth occurs in the colon or rectum, it is called colorectal cancer (CRC). Combined, the colon and rectum make up the large intestine, also sometimes called “bowel”, which is the last part of the gastrointestinal (GI) system (see figure below). Its function is to complete the processing of food for energy and then to get rid of the body’s solid waste.

The colon has 4 sections:

  • The ascending colon begins with a pouch where undigested food is received from the small intestine, called the cecum. The cecum is situated in the lower right abdomen, and the ascending colon extends upward along the right side of the abdomen.
  • The transverse colon crosses the body from the right to the left side of the upper abdomen. Together the ascending and transverse colon are called the “proximal” colon.
  • The descending colon continues downward along the left side of the abdomen.
  • The sigmoid colon, which is named for its “S” shape, is the final portion of the colon and joins the

    rectum. The descending and sigmoid colon are together called the “distal” colon.

The last 6 inches of the large intestine is the rectum. Despite being close to the anus, anal cancers are classified separately from CRC because they start from a different cell type, and thus have different biological characteristics.

How does colorectal cancer start?

The colon has 4 sections:

  • The ascending colon begins with a pouch where undigested food is received from the small intestine, called the cecum. The cecum is situated in the lower right abdomen, and the ascending colon extends upward along the right side of the abdomen.
  • The transverse colon crosses the body from the right to the left side of the upper abdomen. Together the ascending and transverse colon are called the “proximal” colon.
  • The descending colon continues downward along the left side of the abdomen.
  • The sigmoid colon, which is named for its “S” shape, is the final portion of the colon and joins the

    rectum. The descending and sigmoid colon are together called the “distal” colon.

The last 6 inches of the large intestine is the rectum. Despite being close to the anus, anal cancers are classified separately from CRC because they start from a different cell type, and thus have different biological characteristics.

What are symptoms of colorectal cancer?

Unfortunately, early CRCs often have no symptoms at all. This is why screening is so important. As a cancer grows, it may bleed or block the intestine (obstruction). This can show up with warning signs like these:

  • Blood in the stool or in the toilet after having a bowel movement,
  • Dark or black or even tarry stools (this is how partially digested blood appears),
  • A change in bowel habits (such as more diarrhea or constipation than usual),
  • A change in the shape of your stool (for instance, more narrow than usual),
  • Cramping or discomfort in the lower abdomen, and/or
  • An urge to have a bowel movement when the bowel is empty.

In addition, sometimes blood loss from the cancer over time can lead to anemia, or a low number of red blood cells. This can show up with symptoms such as:

  • weakness,
  • fatigue, and/or
  • shortness of breath.
  •  

What are risk factors for colorectal cancer?

Demographic Factors

 Age

The risk of CRC increases with age. The median age at diagnosis for colon cancer is 68 in men and 72 in women; for rectal cancer it is 63 years of age in both men and women. However, there has been an alarming rise in CRC in younger age groups. CRCs diagnosed in individuals younger than age 50 nearly doubled between 1990 and 2013. But, most of these cases occurred in people who were in their 40s. The reason for this rise is not known, but given the association between CRC and obesity, it is possible that the rise in childhood obesity is a major factor. Hereditary forms of CRC also occur in younger individuals (even before age 40), but there is no evidence that the incidence of hereditary CRC has risen.

Gender
CRC is approximately 30% more frequent in men than in women. The reasons for this difference are not fully understood, but likely reflect differences in exposures to lifestyle risk factors, like tobacco and the Western diet, and sex hormones, and interactions in between.

Race/ethnicity
CRC incidence and mortality rates are highest in non-Hispanic blacks (NHBs) and lowest in Asians/Pacific Islanders (APIs), with incidence in blacks were about 20% higher than in non-Hispanic whites (NHWs) and 50% higher than APIs. CRC death rates in blacks are 40% higher than in NHWs and double those in APIs. Reasons for racial/ethnic disparities in CRC largely reflect differences in socioeconomic status and the relationship with behavioral factors associated with CRC, such as obesity and tobacco use, as well as access to healthcare.

 

Lifestyle Factors

Overweight and obesity
The prevalence of obesity among American adults has more than doubled, from approximately 15% in the 1970s to nearly 40% in 2015. Excess body weight increases the risk of CRC, with a stronger association in men than in women and for colon than for rectal tumors. Specifically, compared to people who are normal weight, obese men have about a 50% higher risk of colon cancer and a 20% higher risk of rectal cancer, whereas obese women have about a 20% increased risk of colon cancer and a 10% increased risk of rectal cancer. The excess risk conferred by obesity is independent of physical activity, and weight gain appears to have a greater influence on CRC risk when it occurs in early adulthood. In addition, excess body weight can have a negative impact on metabolic health, which is the proper functioning of all of the biochemical processes in the body. Therefore, often being overweight is also associated with other diseases, such as hypertension, diabetes, heart disease, and stroke, just to name a few.

Diet
Dietary patterns likely influence risk directly, through the intake of specific nutrients, and indirectly, through overweight and obesity. Diet also has a large influence on the microorganisms in the large intestine, called the microbiome, which plays a role in inflammation and immune response. The role of specific food items in cancer occurrence is very challenging to study for many reasons, including the difficulty defining and measuring intake, the variety of sources of dietary elements, and links between dietary patterns and other health behaviors. However, we provide a brief list of nutrients currently supported by scientific evidence to be linked to CRC:

  • Calcium: Most studies find that dietary calcium from dairy foods and/or supplements is associated with a decreased risk of developing adenomas and CRC. Potential anticancer benefits appear to require several years to observe.
  • Fiber: Although it is highly plausible that dietary fiber decreases risk of CRC for many reasons, including less exposure to carcinogens because of higher stool volume and faster transit time, study results, including those from randomized controlled trials, remain inconclusive. However, because of the overall health benefit of a high-fiber diet, the American Cancer Society (ACS) and the World Cancer Research Fund (WCRF) both advocate a diet high in fiber from whole grains, fruits, and vegetables for the prevention of cancer.
  • Folate: Dietary folate, consumed through food or supplements, appears to have a complex relationship with CRC risk, potentially promoting growth of pre-existing tumors, while inhibiting formation of new tumors.
  • Fruits and vegetables: Like with dietary fiber, results from various studies evaluating the association between fruit and vegetable intake and CRC risk are inconsistent. But, both the ACS and WCRF include regular consumption of fruits and vegetables in a cancer prevention diet.
  • Red and processed meat: Consumption of red and/or processed meat clearly increases the risk of both colon and rectal cancer. The reasons for this association may be related to carcinogens (cancer-causing substances) that form during high-temperature cooking, curing, and/or smoking, or possibly to constituents in the meat itself.
  • Vitamin D: Higher blood levels of vitamin D may be associated with lower risk of CRC, although study results remain inconclusive. Data expected from ongoing clinical trials evaluating the effect of vitamin D supplementation on cancer prevention may help clarify this association.

Physical inactivity
Physical activity is strongly associated with a reduced risk of colon cancer, but not rectal cancer. Studies consistently show that the most physically active people have a 25% lower risk of developing both proximal and distal colon tumors than the least active people. Additionally, people who are more physically active before a CRC diagnosis are less likely to die from the disease than those who were less active. Even sedentary people who become active later in life may reduce their risk. The ACS and Centers for Disease Control (CDC) recommend that adults engage in at least 150 minutes of moderate-intensity activity or 75 minutes of vigorous-intensity activity each week, spread throughout the week.

Tobacco use
In 2009 the International Agency for Research on Cancer (IARC) determined that there was enough evidence to conclude that tobacco smoking causes CRC. The association appears to be stronger for rectal than for colon cancer. Smoking is also associated with lower survival after CRC diagnosis.

Alcohol
Moderate and heavy alcohol use, more than 12.5 grams per day (about one drink), is associated with increased risk of CRC. Compared with nondrinkers and occasional drinkers, people who have a lifetime average of 2 to 3 alcoholic drinks per day have about a 20% higher risk of CRC, and those who consume more than 3 drinks per day have about a 40% increased risk. The association is stronger in men than in women, possibly due to hormone-related differences in alcohol metabolism.

 

 

Personal Medical Factors

Adenomatous colon polyps
Please refer to the section above on “How does colorectal cancer start?” to learn about colon polyps. There are also hereditary syndromes associated with colon polyps. Please see the section below on Genetics, which reviews the importance of family history analysis.

Inflammatory Bowel Disease
Inflammatory bowel disease (IBD) has been diagnosed in an estimated 3.1 million Americans and is most common in NHWs and those with the least education and highest poverty. The most common types of IBD are ulcerative colitis and Crohns disease. People who have chronic IBD, in which the colon is inflamed over a long period of time, have almost double the risk of developing CRC compared to the general population. Cancer risk increases with the extent, duration, and severity of IBD, but has decreased over time, likely due to the more common use of medications to control inflammation. In addition, high-risk screening is very useful for early detection of premalignant lesions.

Diabetes
The number of Americans with diabetes doubled between 1990 and 2012. And, people with type 2 (adult-onset) diabetes have a higher risk of CRC. Although type 2 diabetes and CRC share many risk factors, including obesity and a sedentary lifestyle, this association remains even after accounting for physical activity, body mass index, and waist measurements.

Familial and Genetic Factors

Family History
Up to 30% of CRC patients have a family history of the disease. But, only about 5% of those are due to an inherited genetic abnormality. People with a first-degree relative (parent, sibling, or child) with CRC have 2-4 times the risk of developing the disease compared to people without this family history, and this varies depending on the age at diagnosis and number of relatives involved. Risk is highest for people with multiple first-degree relatives diagnosed with CRC, but risk is also slightly increased among people with a first- or second-degree relative diagnosed with benign adenomas.

Genetics
Much of the CRC clustered in families is thought to be due to the combination of lifestyle factors and their interaction with common genetic variations, as opposed to hereditary syndromes, which account for only about 5% of all CRCs. However, those hereditary syndromes are associated with specific gene mutations and, because most people who have a genetic predisposition for CRC are also at increased risk for other cancers, it is really important to test for those specific mutations in individuals that display a family history pattern suggestive of a hereditary syndrome. Because only 22% of patients with CRC were found to have complete information on family history in their medical records, it is important to seek the expertise of a health care professional with training in cancer genetics who can examine your full family pedigree for these patterns. In fact, it is estimated that only 1% of individuals with hereditary CRC were aware of their syndrome until after they were diagnosed… yet individuals with such syndromes are eligible for special cancer screenings and both medical and surgical interventions that are highly effective for risk reduction.

What Is Your Best Next Step

As complex human beings, often we have a complicated mix of risk factors. To add to that complexity, two individuals with identical risk profiles will often make different risk reduction choices, based on their own risk tolerance and personal preferences.

A 1:1 Outsmart Cancer Consultation will help you tease out your personal history, discover what your risks actually are, and what are your options for living your healthiest, happiest, and longest life. Then, you will be empowered to make well-informed decisions about how you would like to proceed, empowered to take charge of your health! And, because we understand the gap between knowing what to do and actually doing can sometimes be wide, we even offer health coaching support to integrate healthy habits into your busy life. Toscheduleyourconsultationtoday,gohere.

 IfyouwouldliketotakeourFREEcancerriskself-assessmentfirst,gohere.  And,tolearnaboutourhealthcoachingprograms,gohere.

To your health!

With love, Dr. Mel

P.S. Medical references for any of the materials contained in this fact sheet are available upon request. Please note that this information is provided for general educational purposes only and cannot substitute for personalized medical advice.