“If a close relative is stricken with cancer, must everyone in the family undergo cancer screening?”

“Is it true that the earlier we undergo cancer genetic testing, the better?”

“Does removing the entire organ like breasts, ovaries, colorectal or prostate eliminate all risks of cancer?”

Doctors understand that people with a family history of cancer are suffering from lingering fears that they are at risk of developing a hereditary cancer sooner or later. At times, these growing fears and anxiety could cause them to feel restless or even throw them into great disarray, causing them to misinterpret their genetic test result or try certain preventive treatment options that may not be suitable for them. Therefore, before deciding to undergo cancer genetic testing, you may want to ask the following five questions, in order to clarify your understanding of cancer genetic testing, understand the clinical significance of the cancer test results, and then decide on the prevention that is suitable for you.

1. Which type of cancer is your family member diagnosed with?

Theoretically speaking, all cancers can be hereditary, but the probability of the cause of cancer being hereditary varies amongst types. In Hong Kong, breast, ovarian, colorectal and prostate cancers are among the most common types of cancer that are hereditary. About 5%-10% of cases in breast, ovarian and prostate cancers are hereditary, while 3%-5% of colorectal cancer cases are hereditary.

Hereditary breast, ovarian and prostate cancers are mainly related to BRCA1 or BRCA2 genetic mutations. As for hereditary colorectal cancer, the most common forms are familial adenomatous polyposis (FAP) and hereditary nonpolyposis colorectal cancer (HNPCC) (also known as Lynch syndrome). Patients with hereditary colorectal cancer tend to be younger and develop the disease when they are in their early teens. Patients with FAP have adenomatous polyps formed in the colorectal and rectum, which in turn evolve into colorectal cancer over time.

General advice: before you decide to undergo a medical check-up or treatment, you should evaluate your risk of developing a hereditary cancer and the benefits that such test or treatment can bring you. Since not all cancers have a high risk of being hereditary, if the cancer has a rare chance of being hereditary, a cancer screening test might seem unnecessary, clinically speaking. However, if any individual is diagnosed with colorectal, breast, ovarian or prostate cancer, and given that the risk of these cancers being hereditary is relatively high, we suggest that his/her family members should consult their doctor or medical professionals before deciding to undergo a cancer screening test.

2. Does age and gender contribute to a higher risk of contracting hereditary cancer?

As compared to general cancer cases that are related to gene mutations caused by aging, smoking or other environmental factors, hereditary cancers develop relatively early. In one clinical case study, a young woman was diagnosed with breast cancer in her early 30s and her sister, who was in her 20s, discovered from her genetic test result that she was also carrying the BRCA1 or BRCA2 mutated genes that could cause ovarian and breast cancers. BRCA1 or BRCA2 can also be found in men, significantly increasing their risk of developing prostate and breast cancers (breast cancer is not only a female disease).

In addition, the Lynch syndrome associated with hereditary colorectal cancer is characterized by young onset, and families with such family history often have more than one family member with cancer at the same time. More often than not, patients with Lynch syndrome suffer from more than one type of cancer, including 40% to 60% chance of contracting endometrial cancer and about 10% chance of contracting ovarian cancer in a lifetime.

General advice: although there are no clear guidelines in the medical community on the recommended age range for cancer genetic testing, young adults with a family history of cancer are among the high-risk groups and should take a proactive approach towards screening tests as a preventive measure. The earlier they detect whether the body carries cancer-causing genes, the earlier they can develop a plan to further monitor the progress of their disease. They could even consider undergoing a preventive cancer surgery to minimize the adverse impact of the risk of cancer on their lives.

3. How accurate is genetic testing in predicting cancer?

Using the latest NGS technology, current genetic testing is conducted on DNA extracted from a collected sample of blood or saliva, with accuracy close to 90%. However, the “high accuracy” as used herein refers only to the fact that the test results can almost accurately reflect whether there is a mutated gene in the body, and amongst those with mutated genes, not everyone will contract cancer. Take the BRCA1 gene as an example — only about 70% of people with this mutated gene ends up being diagnosed with breast cancer.

General advice: at present, cancer genetic test results mainly serve as a reference; they may be viewed as a warning but should not be used as the diagnosis standard. Therefore, you need not be too worried even if your cancer genetic test result is positive.

4. How willing are you to undergo preventive cancer surgery?

As mentioned above, besides serving as a warning, the result of preventive genetic testing for cancer could be one of the key considerations for people at high risk of cancer to decide whether a preventive surgery should be undertaken. Taking preventive breast, fallopian tube and ovary removal surgery as an example, preventive surgery could reduce the probabilities of individuals with BRCA1/2 mutated genes developing breast and ovarian cancers by 90% and 85%, respectively.

In the aforementioned case involving the two sisters, the younger sister, who carried BRCA mutated genes but was yet to be diagnosed with cancer, opted to have her breasts surgically removed so as to reduce the risk of developing cancer in the future. Undertaking preventive surgery is a personal choice that involves consideration of many other factors beyond health; after all, even if we have genes that are potentially cancerous, chances are that they might not develop into cancer. For married women, they may mind how their partners think of themselves, and the fear of losing their gender identity and becoming less attractive to their partners after breast removal surgery is a key reason for not pursuing preventive surgery. Studies have demonstrated that in Asia, most women prefer to undergo regular screening tests or take medications as a preventive option to reduce their risks of developing breast and ovarian cancers.

General advice: If you undergo cancer genetic testing out of curiosity, it is likely that you would be consumed by immense psychological stress. Therefore, before undergoing genetic testing, you should consult a genetic counsellor and let him/her know your family history and personal concerns fully, so as to ensure that you are well-informed and ready before undergoing cancer genetic testing. With the assistance of a multi-disciplinary professional medical team, the genetic counsellor can offer comprehensive advice on cancer risk management, including cancer risk evaluation for first-degree relatives and preventive treatment options available, to prepare those at a high risk of cancer before a decision is made.

5. Do you regularly undergo body check-ups?

Even if preventive genetic testing for cancer or preventive cancer surgery has been undertaken, it does not mean that all risks of cancer are eliminated for the future; it is necessary to undergo body check-ups on a regular basis.

General advice: in general, women aged above 40 are recommended to undergo breast cancer screening once every two years. For high-risk groups with a family history of cancer, it is advised that they undergo breast cancer screening frequently from the age of 18; according to the doctor’s recommendation, they should undergo a clinical breast examination twice a year and a mammogram, breast ultrasound and MRI once every 1 to 2 years from 25-30 years old onwards. For men, those with mutated genes should undergo regular breast and prostate cancer screening with prostate-specific antigen (PSA) test and digital rectal exam (DRE) examination at least once a year.

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Dr. Tsang Wai Kong, Maverick

SPECIALIST IN CLINICAL ONCOLOGY