By Dr Bhupinder Mann, Senior Consultant
& Dr Peter Ang, Associate Consultant Department of Medical Oncology,
NCC
Cancer is a common disease,
and majority of the cases are sporadic. Purely by chance, many cases
of "common" cancers, e.g. breast, colon and lung cancers can appear
to run in a family. Other risk factors which are not genetic such
as diet, smoking and environmental exposures can also lead to clustering
of cancer cases within a family.
However, in some families, multiple cases of cancer can occur in several
generations or at younger ages. In these circumstances, genes carrying
harmful alterations may be involved. Since there is no simple genetic
screening test available presently that can determine this, a detailed
3-generation family history is the starting point to assess an inherited
risk of cancer.
If history makes one suspect an inherited cancer, then one can consider
genetic tests starting with an affected family member. Currently,
these tests are labour-intensive and costly, and are positive in only
about 50% of the affected families. So even if the test is negative
in an affected family with strong suspicion for inherited predisposition
to develop cancers, it does not mean that one can do away with the
need for close follow-up.
Testing positive for an alteration in the DNA may raises the probability
of developing a certain type of cancer however it is not a prediction
that an individual will develop cancer. The potential benefit of a
positive genetic screen depends on the availability, acceptability
and efficacy of increased surveillance techniques and preventive options
such as prophylactic surgery or chemoprevention (using medication
to prevent or reduce the risk of cancer). Such benefits may be magnified
when there are several at-risk family members willing to be screened
for a specific cancer causing mutation. Given the complexity and uncertainty
on genetic screening, referral to a health care professional with
interest in familial cancers should be considered. Appropriate referral
enables an individual to discuss the risks and benefits of testing
that would lead to making an informed decision on genetic testing.
When these individuals seek counseling and management at NCC's Risk
Evaluation and Prevention (REAP) Clinic, a detailed family history
is taken first to assess the risk of a hereditary cancer affecting
the family. If a suspicion is raised, then risks and benefits of DNA
based testing are discussed at length. Decision to undergo such testing
is complex and has to be made by a family after careful consideration
of all the pros and cons. For more information about the REAP Clinic,
please call the Cancer Helpline on tel: 622-55-655.
