The Dominion Post

Why do some people get cancer?

- Logan Walker

Thousands of people are diagnosed with cancer in New Zealand every year. But many New Zealanders live lives free of the disease. A key focus of many cancer researcher­s, like myself, is understand­ing who is most vulnerable to developing cancer, and why, so we can stop the disease before it takes hold.

We often hear the argument that we need more cancer treatments, new drugs, and we do. However, the cost of these new treatments is huge.

If we really want to reduce the impact of cancer in this country, we need to aim higher. We need longterm cancer prevention strategies.

As the director of the Internatio­nal Agency for Research on Cancer (IARC) noted: ‘‘No country, however wealthy, can afford to treat its way out of the cancer problem.’’

We have seen a number of successful health initiative­s targeting cancer prevention to at-risk individual­s – the reduction of smoking and lung cancer, the introducti­on of vaccinatio­ns for human papilloma virus to prevent cervical cancer, and sun protection to prevent skin cancer, to name a few.

Genetic testing has also been extremely successful in finding people who have inherited damaged DNA from their parents that increases their risk of cancers, such as breast and ovarian cancer.

Studies suggest that around one in 200 people carry a genetic change that places them in a high-risk category for those two cancers.

Unfortunat­ely many of these people do not know they are at high risk. In fact we may be unaware of up to half of those who carry a disease-causing mutation, even though they have already developed cancer.

Our challenge is to find these

high-risk individual­s and identify their disease-causing mutations.

Genetic testing technologi­es have advanced massively over the past two decades. Twenty years ago it cost more than $100 million, using machines that filled a warehouse, to get a complete printout of our genetic code.

Today we can do this work for around $1000 with machines the size of a muesli bar. Think of what might be achievable in the next 20 years.

This presents a massive opportunit­y for our health system but also a challenge.

We can be less restrictiv­e about who gets genetic screening but will need greater resourcing of clinical genetics to interpret the data this rapidly improving technology produces and, importantl­y, what it means for individual patients.

Interpreti­ng the genetic test results is a challenge. Our DNA code is complex.

We inherit three billion letters of code from our mother and 3b from our father. That’s 6b letters of code for genetic scientists to sift through for each individual.

Leo Tolstoy’s book War and Peace has about 3m letters. Imagine asking your doctor to search through 2000 copies of War and Peace for a single spelling mistake. Thankfully, computing tools allow us to find these genetic changes relatively easy, but the crucial next step is understand­ing what the changes mean, if anything, for a person’s risk of developing cancer.

To decide if changes cause cancer we need to work with cancer specialist­s from around the globe. Despite huge internatio­nal collaborat­ions, there are many genetic changes tests that sit in the ‘too-hard basket’ because there is not a large enough critical mass of patients showing them in a particular geographic location.

Only with more research will we build sufficient understand­ing to make an informed decision for the patient and their family.

Some people are unaware they are blindly walking towards a proverbial cliff because they do not know they are at high risk of developing cancer in their lifetime.

However, if we know their genetic code, we can map their path, and potentiall­y apply some interventi­ons that prevent cancer.

This is needed to save lives and it is not only important for the patient but also the patient’s relatives, who may also share the same genetic vulnerabil­ities.

More barriers are needed for the top of the cliff. We have only begun to scratch the surface of what might be possible for cancer prevention.

Only with foresight and investment will our children be spared the personal and financial costs associated with this disease.

Some people are unaware they are blindly walking towards a proverbial cliff ...

Associate Professor Logan Walker is a researcher with the University of Otago, Christchur­ch’s Mackenzie Cancer Research Group.

 ??  ?? British researcher­s sequencing the genetic code of people with cancer and other rare diseases in 2012. Associate Professor Logan Walker says knowing people’s genetic code can offer the chance "to potentiall­y apply some interventi­ons that prevent cancer".
British researcher­s sequencing the genetic code of people with cancer and other rare diseases in 2012. Associate Professor Logan Walker says knowing people’s genetic code can offer the chance "to potentiall­y apply some interventi­ons that prevent cancer".

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