Colorectal cancer is the second leading cause of cancer death in Canada, after lung cancer, and is the fourth most commonly diagnosed cancer in Canada after prostate, lung, and breast cancers. The Canadian Cancer Society estimates that Canadian physicians will diagnose 22,200 new cases during 2011, half of whom will not have symptoms until the advanced stages of the disease, and 8,900 Canadians will die from the disease this year, usually because of detection in the advanced stage. Colorectal cancer accounts for 13% of cancers diagnosed in men and 11% of cancers diagnosed in women.1
CRC and Diabetes
In a recent study that followed more than 150,000 older adults for up to fifteen years, researchers found that men who have type 2 diabetes are at a moderately higher risk of developing colorectal cancer than those without diabetes.2 The increased risk was not found in women. This association is especially important considering the high mortality rates of colorectal cancer and the rapidly increasing worldwide prevalence of type 2 diabetes, even among adolescents.
Type 1 diabetes, usually diagnosed in children and adolescents, occurs when the pancreas is unable to produce insulin. Insulin is a hormone that controls the amount of glucose in the blood. Approximately 10% of people with diabetes have type 1. The remaining 90% have type 2 diabetes, which typically develops in adulthood and occurs when the pancreas does not produce enough insulin or when the body does not effectively use the insulin that is produced. Although type 1 diabetes is always treated with insulin, type 2 diabetes is managed through physical activity and meal planning and may require medications and/or insulin to assist the body in controlling blood glucose more effectively.
In 2000, there were approximately 171 million people with type 2 diabetes worldwide, and by 2030 that number is projected to almost triple.
The study’s findings, published in the journal, Gastroenterology, reinforce current recommended guidelines for early detection screenings for colorectal cancer in men who have longstanding type 2 diabetes. A further implication from the report is that maintaining normal blood glucose and insulin levels could be key factors in preventing colon cancer.
The study began in 1992 with participants 50-74 years of age who completed questionnaires approximately every two years, which included information about cancer screening, medical history, diet, smoking, and other factors. The final analysis included 73,312 men and 81,663 women, but did not include anyone with type 1 diabetes.
On completing the study, researchers found that men with a history of type 2 diabetes were associated with a 24% higher risk of developing colorectal cancer than men without diabetes. Although those men who reported insulin use had a slightly greater risk of developing colorectal cancer than those using oral medications, the study authors note this result is not statistically significant. Insulin use might be a relevant factor, and the study authors suggest that more research is necessary, since many people diagnosed with type 2 diabetes eventually require insulin.
Other recent studies support an association between type 2 diabetes and colorectal cancer in men. The risk of developing colorectal cancer in men increased the longer that patients had type 2 diabetes, with almost no association until after having the disease for at least ten years. Older studies showed similar results, but for both men and women equally. Starting in the 1990s, there was an increase in the prescribing of metformin (a drug used to control blood sugar levels in type 2 diabetes) specifically to women and the researchers speculate that the reduced colorectal cancer risk demonstrated for women with type 2 diabetes in the current study might be related to better glucose control associated with the use of this medication. A further implication of this is that blood-sugar management in general may affect a person’s risk for developing colorectal cancer.
Research in this area is ongoing, and those who have type 2 diabetes are encouraged to follow the same guidelines for preventing colorectal cancer as those for the general population. These include early detection exams, as well as smoking cessation, a healthy diet, weight management, and exercise.
Labrador Laboratory Assistant
The wonder of canine colon cancer detection and what it could mean for future early detection methods.
In a recent study published in the journal, Gut3, researchers in Japan compared an 8-year old female black Labrador’s ability to detect colon cancer with that of a standard testing method looking at fecal occult blood samples. They used colonoscopy diagnosis as the measure of accuracy.
The study’s samples came from patients known to have colon cancer, including a range of stages of the disease, and from a control group made up of people who did not have cancer but who may or may not have a history of cancer. In each test group, researchers tested one sample from a person confirmed to have colon cancer alongside four people from the control group. The samples studied included 37 groups of watery stool and 33 groups of exhaled breath.
This was a double-blind study, which means the samples were anonymous to the dog, the handler, and even the laboratory assistants. The dog, which was already trained in detecting various cancers, would smell a standard breath sample from a person with colon cancer before entering a room containing only five boxes of study samples lined in a row. She would then pass by the ones she believed were not from cancer patients and sit down in front of the box she believed was positive for colon cancer. The dog’s handler would then fill out an answer card and fax it to researchers in another area of the facility, after which the researchers would reply with the correct answers so that the handler could reward the dog’s correct detections with a tennis ball.
The dog’s accuracy was extremely high, with only one discrepancy between colonoscopy in the watery stool samples and three discrepancies in the breath samples. The dog’s overall accuracy ranged from 91-99%, and was significantly higher than fecal occult blood testing for early detection. Other researchers have shown similarly promising results testing the ability of dogs to detect other types of cancer, such as lung, breast, bladder, and ovarian.
The researchers say this test shows that a unique cancer scent must exist, made up of cancer-specific compounds called volatile organic compounds (VOCs) that may circulate throughout the body. Future studies will focus on identifying those compounds. The success of this study does not lead the researchers to endorse using dogs as a new method of cancer detection because the time and expense involved in training and working with such dogs would be extremely expensive and impractical. Instead, they hope future scientists will develop an early detection sensor as a reliable substitute for the canine’s natural expertise.
About 5% of colon cancers are associated with genetically defined colon cancer family syndromes, and 20-30% of all colon cancers have a potentially definable inherited cause.