Haze is also a risk factor for lung cancer

The Jalan Toa Payoh stretch of the Pan-Island Expressway obscured by the haze in September last year.
The Jalan Toa Payoh stretch of the Pan-Island Expressway obscured by the haze in September last year. PHOTO: ST FILE

Q Should I go for lung cancer screening? What is involved and what are the risks?

A A large percentage of lung cancers are diagnosed in the advanced stage where it is usually incurable, although there are many advances in drugs that have been shown to prolong survival.

If the cancer is diagnosed or found earlier, perhaps a higher number of patients can be cured.

This is where cancer screening comes in. While screening has a proven track record for breast, colon and cervical cancers, there is still some debate on whether lung cancer screening is useful.

Evidence for this came from a very large randomised study called the National Lung Screening Trial (NLST), conducted in the United States and involving more than 50,000 smokers or former smokers aged 55 to 64.

They were considered high risk and eligible for the study if they had smoked 30 pack-years (equivalent to one packet of cigarettes a day for 30 years).

Former smokers would need to have quit any time within the previous 15 years.

Half of the group had a low-dose computed tomography (CT) scan performed annually for three years while the other half had chest X-rays done.

False-positive (false alarm) results can lead to follow-up tests and surgery which may involve more risks, and the patients may turn out not to have cancer in the end.

After a period of follow-up for seven years, it was found that the CT-scan group had a 20 per cent lower chance of dying from lung cancer compared to the X-ray group. In other words, more lives can be saved if CT scans are done as a screening test.

While this sounded very positive, there were limitations to such an approach. False-positive (false alarm) results can lead to follow-up tests and surgery which may involve more risks, and the patients may turn out not to have cancer in the end.

The definition of "high risk" smokers and the age groups to be screened are also subjects of contention.

In addition, there are risks associated with radiation exposure from the scans and no one knows what is the optimal duration that a person should continue to be screened.

More importantly, if you feel you may have an increased risk of lung cancer from smoking, then the first step is to stop smoking. This is usually easier said than done.

Unfortunately, people who are exposed to second-hand smoke also have a 20 per cent higher chance of getting lung cancer.

The haze is also another risk factor, as air pollution is now recognised as a carcinogen (cancer-causing agent).

It is best to talk to your doctor regarding your risks of getting lung cancer, and the advantages and disadvantages of going for lung cancer screening, especially if you match the characteristics of the group that was recruited in the study above.

Dr Ooi Wei Seong

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The Jalan Toa Payoh stretch of the Pan-Island Expressway obscured by the haze in September last year.

A version of this article appeared in the print edition of The Straits Times on June 21, 2016, with the headline 'Haze is also a risk factor for lung cancer'. Print Edition | Subscribe