When most people think about cancer, they think about the 'gruelling' treatment. As a medical oncologist, I often see patients after cancer has developed. By then, our focus is on controlling the disease rather than preventing it. But what if we could identify cancers before they develop?

This is where cancer genetics comes in. A common misconception is that genetic testing inevitably leads to preventive surgery. While high-profile cases such as Angelina Jolie's brought attention to hereditary cancer risk and preventive surgery, cancer genetics and patient management strategies have evolved considerably over the past decade.

While most cancers occur sporadically, around 5 to 10 per cent are linked to hereditary cancer syndromes that can be passed from one generation to the next. Hereditary cancer syndromes significantly increase a person's risk of developing certain cancers, but they remain under-recognised and underdiagnosed.

In fact, research conducted in Singapore found that only 17 per cent of patients who meet the criteria for genetic testing are referred for assessment. This means more than 80 per cent of high-risk individuals may be missed. These are missed opportunities for prevention, early detection and better outcomes for patients.

One of the most important clues hiding in plain sight is family history. Family history is one of the most powerful tools we have for identifying hereditary cancer risk. It can provide an early warning sign, allowing individuals and families to take action before cancer develops.

When assessing a patient's risk, we look for patterns such as multiple relatives diagnosed with cancer, cancers occurring at younger ages than expected, or individuals who develop more than one type of cancer. These can all be signs of a hereditary cancer syndrome.

The most common hereditary cancer syndromes we see at the National Cancer Centre Singapore's Cancer Genetics Service are Hereditary Breast and Ovarian Cancer syndrome, often linked to BRCA1 and BRCA2 gene faults, and Lynch syndrome, which is associated with colorectal and uterine cancers. Increasingly, we are also recognising hereditary links in other cancers, including kidney cancers and sarcomas.

Understanding these risks allows us to shift from reactive care to proactive care.

Traditionally, healthcare has focused on treating cancer after it develops. Genetic testing enables us to identify individuals at increased risk of developing cancers and intervene earlier. If we know someone carries a cancer-predisposing gene fault, we can recommend personalised screening plans, more frequent surveillance or preventive measures to help detect cancer at its earliest and most treatable stage.

Importantly, the impact extends beyond a single patient.

When a hereditary cancer syndrome is identified, family members may also be at risk. First-degree relatives, including parents, siblings and children, often have a 50 per cent chance of carrying the same gene fault. This means one diagnosis can provide critical information that helps protect an entire family.

Many people assume that genetic testing will lead to preventive surgery, but this is not always the case. Cancer genetics has evolved considerably over the past decade, and we have more options today. For individuals with hereditary cancer syndromes, enhanced surveillance can also be an effective management strategy. Regular screening allows us to monitor high-risk patients closely and detect cancers early, often without the need for radical preventive surgery.

Genetic testing is also increasingly shaping cancer treatment. Certain inherited gene faults can assist doctors in predicting how patients respond to therapies, including targeted treatments and immunotherapy. This allows us to tailor treatment strategies more precisely for each patient to ensure the best possible treatment outcomes.

As genetic testing becomes more affordable and accessible, many people ask whether it should become part of routine health check-ups.

Genetic testing is not part of routine health check-ups because it measures disease susceptibility rather than providing a definitive diagnosis, which can cause unnecessary psychologic distress, and unneeded follow-up tests. Genetic tests need to be cost-effective, clinically meaningful and supported by appropriate counselling and follow-up care. Identifying individuals who are most likely to benefit from genetic screening is key.

We often compare genetic testing to driving at night with your headlights on. The road ahead may contain obstacles, but with headlights on you can see them coming and navigate around them. Similarly, by identifying cancer risk through genetic testing, we have a better chance of preventing cancer, detecting it early and ultimately saving lives.

So for now, my advice is simple: know your family medical history and talk to your doctor who can advise if you need genetic testing.

(By Clinical Assistant Professor Chiang Jianbang, Consultant, Division of Medical Oncology, National Cancer Centre Singapore)

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