Proof is key to science, which can thereby make a lot of demands. As a doctor, I do subscribe, by and large, to evidence-based medicine - the practice of rigorous and repeated tests, clinical trials and journal reviews.
I hardly ever make a statement without scientific proof. However, I believe there is at least one notable exception: Stress causes cancer, even though I cannot prove it.
This is not from lack of trying. Others too have long tried to correlate stress to cancer.
Over the past 30 years, studies that examined the relationship between psychological factors (including stress) and cancer risk have been inconclusive. Although the results of some studies point to a link between various psychological factors and an increased risk of cancer, a direct cause-and-effect relationship has not been established.
With 26 years of medical experience, I offer some hypotheses, albeit without firm scientific proof.
Whenever one of my patients has cancer recurrence, I gently probe into what is going on in his or her life. Often, those who open up talk about unfaithful husbands, money problems, unhappiness at the workplace or problems with children and their studies.
Recently, a pleasant woman came to see me with her husband, after having been diagnosed with advanced stomach cancer. One of her questions was: 'Why did I get stomach cancer?'
There are many possible causes for this cancer, like preservatives in food, carcinogens from smoked or barbecued meats (which happens to be one of my favourite foods) or Helicobacter pylori (a bacterial infection of the stomach). I also suggested to her that stress might be a factor.
Although she did not say anything, the way she turned to look at her husband spoke volumes. Her husband nodded, agreeing that she was indeed going through a stressful time.
Such anecdotes are unscientific and I can understand why it is difficult to prove that stress causes cancer. After all, two individuals can be doing the same stressful work. Yet one may thrive on the excitement of the work intensity while the other struggles with the same workload.
I remember a conversation in 1992, when ProfessorSun Yan, a renowned oncologist from Beijing, visited Singapore. He was asked whether he believed that stress can cause cancer. Without hesitation, he said: 'Of course, stress definitely causes cancer.'
I was taken aback and asked him why he gave such a confident response. He went on to talk about the Cultural Revolution in China.
During that period, between 1965 and 1975, ordinary Chinese people came under tremendous psychological stress. Betrayal by friends and family, oppression of thought and mandatory and harsh new routines created an upheaval in their lives.
'During that period, I was already a doctor and there was a sudden rise in the number of cancer patients in all the hospitals,' Prof Sun related.
'We saw many more cancer patients. The common factor among them was the tremendous psychological stress they were all experiencing. That's why I'm sure that stress is one of the causes of cancer.'
At the time, I had doubted his conclusion. Today, after more than 20 years in the field of oncology, I am more inclined to believe him.
So how does stress cause cancer?
Evidence from animal and human studies has shown that chronic stress weakens the immune system which is responsible for constant surveillance within our bodies for infections and cancers.
This system seeks out and destroys abnormal cancer cells which may arise from time to time. When it fails, the cells can go undetected and grow into malignant tumours.
For the same reason, patients suffering from Acquired Immunodeficiency Syndrome, or post-kidney transplant patients on immunosuppressive drugs, are more prone to developing certain cancers.
There is also some data suggesting that cancer patients who feel helpless and have negative emotions tend to be worse off. The 'bad vibes' promote the growth or spread of cancer, although this relationship was not consistently seen in all the studies.
So how can anyone, particularly a cancer patient, cope with stress?
Faith in God is one way. By entrusting one's life to a supreme being, the burden is taken off oneself. Exercise, meditation, leisure activities, counselling and use of anti-anxiety drugs may all help in improving one's psychological well-being too.
Even though I sometimes struggle to see the many patients waiting to see me, I constantly remind myself to practise what I preach: 'Be happy and live each day to its fullest'.
You don't need science to tell you that.
angpt@parkwaycancercentre.com
Dr Ang, the medical director of Parkway Cancer Centre, has been treating cancer patients for nearly 20 years. In 1996, he was awarded Singapore's National Science Award for his outstanding contributions to medical research.
This story was first published in Mind Your Body, The Straits Times, on Dec 18, 2008.
