Living in a probabilistic world

Living in a probabilistic world

Whenever I give a talk on "Smoking and Cancer", one question inevitably pops up. "Doctor, my grandfather smoked 40 cigarettes a year for 60 years and he never contracted lung cancer. Can you comment on this, please?"

Sometimes, the tone of the questioner's voice is laced with disbelief. Does smoking really cause lung cancer? Not infrequently, the questioner is a smoker himself and is trying hard to justify his bad habit. There are times when there is a genuine desire to learn.

The short answer is: "Smoking greatly increases your risk of lung cancer. For 100 non-smokers, two will get lung cancer in their lifetime. For 100 heavy smokers, 20 will be diagnosed to have lung cancer and almost all 20 will die from it. The link between smoking and lung cancer was unequivocally proven decades ago."

A corollary question is: "Doctor, my sister is a non-smoker, teetotaller and also not married (where did this come from??), and yet she has been diagnosed to have lung cancer. How is that possible?"

Here is the longer answer to both questions.

Risk is not certainty. There is seldom a "one on one" nexus between any risk factor and a negative health outcome. Heavy smoking, excessive alcohol consumption, eating heavily fat- and calorie-laden foods three times a day, and a sedentary lifestyle are all risk factors for cancer, and heart disease. You can hear the naïve and wishful-thinking saying, "My uncle is obese, plays Farmville and other dumbing-down games the whole day long on his iPad 2 and snacks on tons of fries and tomato ketchup. Yet he is alive and kicking."

He won't be both for long, I assure you.

In almost all diseases there are susceptibility genes. We now know there are three sets of susceptibility genes for lung cancer. These susceptibility genes may be inherited from your biological parents or they may be acquired. Environmental factors can alter the genes you are born with or their expression. The way you were brought up as an infant and child (way beyond your control) is an important environmental factor. Even more important is smoking.

The first set of these genes determines your inherent risk of getting lung cancer. The second set has to do with DNA repair mechanisms. Some cancer patients have genes that are faulty and do not sufficiently repair the damage done to the DNA of the cells in their lungs.

The third set of cancer susceptibility genes codes for factors that make you acquire the smoking habit and your addiction potential.

What does all this mean? Well, if you do not have the lung cancer susceptibility genes (not possible to know by routine tests at present), you may not get lung cancer even if you are a heavy smoker. But heavy smoking will, in all likelihood, lead to other cancers (mouth, larynx, oesophagus, stomach, bladder, kidney), heart disease and obstructive airway disease (bronchitis, emphysema), which are major killers by themselves.

If you do not smoke and have a high genetic susceptibility (sets 1 and 2 genes overexpressed), you may get lung cancer if you are the unlucky two in 100.

What can you do if you are diagnosed with lung cancer? Go for the best treatment money can buy. There is some good news. The majority of non-smokers who get lung cancer will do well with conventional chemotherapy, as well as the new relatively costly molecular drugs like gefitinib, erlotinib and crizotinib.

Instead of an average life span of eight months (in smokers with lung cancer), non-smoking patients with lung cancer, especially in those with the "activating" or "good" mutations in their tumours, can live an average of 24 months with current anti-cancer drugs.

The short answer, the longer answer, and now, some philosophical musings. I said that the causative or risk factor of a disease is not "one-on-one". No risk is absolute. Only the simple and literal-minded see the world as black and white.

I am a relativist even in questions of ethics and morals. I am a moral relativist as opposed to the Man With The Golden Ring, who is a moral absolutist.

I have often heard it said that because science cannot provide all the answers, we must look to the realms of fantasy, fiction and faith. But cosmology, quantum physics and evolutionary biology have given me a satisfying, albeit provisional, picture of the universe.

It makes an uncertain world less uncertain. It is a probabilistic world we live in. Science may not reveal the ultimate truth but at least it gives me honest, penultimate answers. It is good enough for me for now.

All or nothing at all? Not me. I will make do with the answers science provides me - be it the treatment of cancer or hypotheses about the beginning and end of the universe - as I continue my search.

For all the cliché that it is, it is no less true. The journey, not the end, is all there is: its inadequacies, disappointments, triumphs, and glories.

Come, walk with me.

Dr Albert Lim Kok Hooi is a consultant oncologist. For further information, e-mail starhealth@thestar.com.my. The information provided is for educational and communication purposes only and it should not be construed as personal medical advice. Information published in this article is not intended to replace, supplant or augment a consultation with a health professional regarding the reader's own medical care.

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