MD_Anderson

There are many advances taking place to make colorectal cancer screening less invasive. Currently, there are tests to identify even small amounts of blood or presence of altered DNA associated with colorectal cancer in the stool. The newest tests are highly sensitive for identifying cancers but are not as good for detecting polyps that have not yet turned into cancer. It is important to identify polyps before they turn into cancer so that they can be removed.
Currently colonoscopy is the best way to identify pre-cancerous polyps and remove them before they can develop into cancer. In another answer, Dr. Morris has also described emerging technologies in blood-based tests using circulating tumor DNA. Although a colonoscopy will still be required after a positive non-invasive stool or blood based test, in order to confirm the diagnosis and to find the cancer within the colon, ongoing advances in non-invasive testing will mean that in the future, more people can be screened for colorectal cancer without the need for colonoscopy. - Dr. Chang

Another red flag would be unexplained changes in bowel habits, such as changes in stool caliber. But sometimes there may be few symptoms, which is why it is important to pay attention to our bodies and seek medical attention should such symptoms develop. - Dr. Chang
I think that the symptoms that people may experience when they present with colorectal cancer are often very similar to other, more benign medical conditions that do not have anything to do with cancer and may sometimes delay the diagnosis of colorectal cancer. Given this troubling trend of rising cases of patients with early-onset colorectal cancer, I think that people having knowledge and awareness of symptoms associated with colorectal cancer - like worsening fatigue, unexplained anemia (low red blood cell counts), bloating in the abdomen, change in bowel habits, for example, especially if they do not go away, should prompt people (regardless of age) to seek further assessment with their medical provider. - Dr. Morris

I was diagnosed at the age of 19 (fresh out of high school!). I noticed my stool had blood in it at one point and, like what most young people do, I googled it. When I saw the frequent answer of colon cancer, I was in denial since it was so common to see colon cancer in older folks. I just believed that I probably ate something bad. I continued to put it off and as more time went by, I noticed how easily I would get tired and would get constant headaches/nausea. After four months, I finally convinced myself to go get checked and sure enough, I had a tumor the size of a golf ball in my colon. After that, it was just a snowball effect of one thing after another to get my health back on track. - Abigail

We are sorry to hear about your aunt. This is a very good question and one that we get asked A LOT. Certainly many of the symptoms associated with colorectal cancer can be similar to other medical conditions, or, as you mention, side effects of certain medications. I think this is one of the reasons it is important to have perhaps a heightened concern when someone notices that, while on a certain medication (citing your example), symptoms start to change while on the same dose.
So, if you been on the same dose of metformin for a while now, and you notice that your appetite is getting even worse or your bowel patterns seem different and don’t seem “normal” for you, then it is important to mention this to your provider in order to make sure there are not other conditions/processes going on in your body, beyond other conditions you may be getting treated for. - Dr. Morris

We don’t fully know, but it may be associated with a number of environmental and lifestyle factors. Recently, we are learning more about the role of the gut microbiome as well. - Dr. Chang