colon cancer: is my son at risk?

My mom was diagnosed with colo-rectal cancer 5 years ago. It was caught early enough to where she just needed surgery to remove the tumor and 8 inches of her colon, but did not need chemo or radiation. She was 44 years old when she was diagnosed.
Six months after her diagnosis, her sister (my aunt) was diagnosed with stage 2 breast cancer. She had a few months of chemo, recovered, and has reached the 5 year remission mark this year. I think she was 38 when she was diagnosed.
Their mother (my maternal grandmother) has been diagnosed with a type of leukemia that is apparently not dangerous to her health; her doctor said she'll most likely die of old age before the leukemia kills her (she's 74, I think, and in good physical health).
I have IBS with constipation, and last month I went to see a gastroenterologist due to concerns of blood in my stool (which is what my mom had to concern her to get a colonoscopy). The doctor found one polyp and did a biopsy on it. It happened to be a pre-cancerous polyp and he said it probably would've turned into cancer in about 10 years. I'm 22 years old, so this gave me a scare--needless to say, I'm a little more attentive to my diet now and eating practically no red meat.
I have a 2 year old son, and I'm wondering what the chances of him getting colon cancer or some other type of cancer might be. As far as his father's side of the family, I don't think there is a cancer risk (my son's father and I are not together, and I don't know a lot of health details about his family). If my son could be at risk, I'm worried about his age and when his risk will be greatest. My mom had colon cancer at 44, my aunt had breast cancer at 38, and I had a pre-cancerous polyp at 22. Should I be concerned for his teen or early 20's years?
How can I find out if he has a genetic cancer risk? I want to do everything I can to keep him healthy.

[Lisa Kessler, MS, CGC]

Whenever more than one close family member is diagnosed with cancer before the age of 50, a red flag goes up. There is a chance that what you are describing in your family is due to an inherited cancer gene.

I recommend seeing a genetic counselor who specializes in cancer risk assessment. He or she will review your family history in detail, get medical records on yourself and your family members (with their permission), and determine what cancer gene, if any, seems most likely. Genetic testing is available for many inherited cancer genes.

The advantage to understanding your risks and possibly having genetic testing are to determine the screening and proactive treatment options (if any) for yourself and your son. Like all moms you are putting your son first, but you need to make sure that you have the proper risk information and  health screening in place for yourself, first. Once you get your own risks squared away, you can focus on your son and determine if there is a medical need to do cancer screening or genetic testing for him before he is an adult, or if you can wait and let him make his own decisions when he is 18.

You can find a genetic counselor at the National Society of Genetic Counselors.