Illustration By Colin Spence
When cancer is prevalent in one’s family – Uncle Burt has had testicular cancer, cousin Georgia found a lump in her breast or Grandpa Ted passed away from stomach cancer – people often say “cancer runs in my family.” Fortunately, cancer doesn’t work like that. It doesn’t so much run as it saunters along, looking in all the store windows and stopping to chat with the passing townspeople.
In most cases, even a high incidence of a certain type of cancer in a family doesn’t mean any one member is at risk. However for those cancers – breast, ovarian and colorectal – where genetic links were discovered in the 1990s, a diagnosis for you or someone in your family may result in referral for genetic counselling and testing, and collecting a complete family medical history.
“People don’t always have 100 per cent accuracy in their knowledge of their family history,” says Dr. Dawna Gilchrist, professor and clinical geneticist at Edmonton’s Medical Genetics Clinic. If you are concerned about your risk for hereditary cancer (see sidebar on page 28), “Talk to your family doctor or specialist,” advises Gilchrist. For those patients that meet the criteria, a referral to the Medical Genetics Clinic is the first step in cancer risk assessment, genetic counselling and possible genetic testing.
If you meet the clinic’s stringent criteria, then you will be contacted by the clinic to confirm interest in pursuing counselling and testing.
Next, the family history must be documented, and then a pedigree is constructed so the clinic can decide whose records they require. “We need records on your mom, your sister and your cousin Georgia (who had the lump in her breast),” says Gilchrist. “We’ll send you release of information forms and then you ask your mom, your sister, and your cousin, ‘Are you willing to sign these medical release forms so that Medical Genetics can review your history?’”
The records are then reviewed and checked against what you have said and if everything still meets the criteria, an appointment is made. According to clinic protocol, the first appointment involves “assessment of hereditary cancer risk, discussion of potential molecular testing including risks/benefits/limitations and recommendations for clinical management.” Also, if you are still interested, the clinic will begin genetic testing by administering a blood test. “DNA is extracted from blood,” explains Gilchrist, “and we look for mutations in specific genes.”
The results of the blood test are revealed at the second appointment, and if they show a genetic mutation, there will be further discussion regarding genetic cancer risk and recommendations for clinical management will be given.
Cancer may be passed on in a family through the mutation of a single gene. For example, says Gilchrist, “Everyone in the world has a pair of BRCA1 and BRCA2 genes. We’re not looking for the presence or absence of those genes, because everybody has them; we’re looking for mutations in one or the other of those genes.”
Gilchrist stresses there are pros and cons to pursuing genetic testing and it is not a decision to be taken lightly. One benefit may be an earlier cancer diagnosis thanks to more frequent screening. Testing also provides patients with the option to take preventive steps such as surgically removing breasts or ovaries before cancers have a chance to form. But there are also possible disadvantages. Because the best way to prevent cancer is not yet known, a patient may wonder exactly what to do with a positive test result for hereditary cancer. Removing the breasts or ovaries will drastically reduce the chances of getting those cancers, but may not totally eliminate the possibility. And even a normal result for genetic testing doesn’t mean that the patient is guaranteed never to have cancer.
Finally, though more attention is given to hereditary breast, ovarian and colon cancers, just about any cancer has a five to 10 per cent chance of being genetic. The two exceptions are cervical cancer (“because cervical cancer is almost entirely due to an infection,” says Gilchrist) and lung cancer, which is “very rare to be seen in a hereditary situation, although can certainly be seen in a family if they’re all smokers.”
Ninety to 95 per cent of cancer is multi-factorial. Contributing factors can come from three domains. Genetics is one domain, but involving your whole body and not just the mutation of a single gene. The other two domains are personal and environmental. Gilchrist breaks it down: “A single gene abnormality like BRCA1 and 2 is like a genetic trump card. All of those other factors still exist but they pale in comparison to the gene mutation. An example of an environmental trump card would be growing up next to Chernobyl. An example of a personal trump card, not for breast cancer, but certainly for lung cancer, would be smoking. It doesn’t matter how healthy you were born or how healthy you otherwise live, if you’re going to insist on smoking, you’re going to have adverse health outcomes.”