Tuesday, April 10, 2012

Singapore - Asians' breast cancer risk different, study shows

A large local study here spanning more than a decade has revealed some startling results: Asian women do not face the same risk of getting breast cancer as women in the West.

Those who have a close relative with this type of cancer are twice as likely to get it, compared with a Westerner. But Asians with no such family history have only half the risk.

So a Singapore woman with a mother, sister or daughter with breast cancer is four times more likely to get it too, compared with someone with no such family history. This appears to be the case across the three major races here.

Previously, based on the Western yardstick, those with family history were thought to have double the risk.

This has major implications on how doctors counsel their patients, said Dr Tan Min Han, the senior researcher in the team. He is a researcher at the Agency for Science, Technology and Research and a visiting consultant at the National Cancer Centre Singapore (NCCS).

The study suggested that women who had a lower risk of getting breast cancer 'would benefit less from the use of mammography'.

On the other hand, women with close relatives afflicted with breast cancer should talk to their doctors and find out how they can reduce their risk of getting the cancer, advised Dr Tan.

One way, if they have got all the children they want, is to remove their ovaries, as this cuts their risk. There is also medicine they can take to lower their risk, he added.

More than 1,550 women get breast cancer each year, and 370 die of it.

The study results were published in the United States-based Breast Cancer Research journal. It is the first such large-scale study done outside of Europe and North America, and has implications for other Asian nations, the authors said.

The NCCS study, started in 1994, tracked more than 28,000 women here aged between 50 and 64 for a decade.

Close to 70,000 women were randomly selected, but only the 28,000 who had no cancer, were not pregnant, and had not had a mammogram or biopsy done in the preceding 12 months were given a single, free mammogram. This was completed by February 1997.

The researchers then checked against the cancer registry at five and 10 years after the mammogram was done.

Cancer reporting is compulsory in Singapore, and with the permission of the Health and Home Affairs ministries, the researchers were able to check if any of the study population had been diagnosed with breast cancer.

Based on the Western model, 362 women from the study group should have contracted invasive breast cancer after five years. But only 144 did. Similarly, 758 women were expected to have the cancer after 10 years, but only 409 did.

The authors concluded that using the Western model 'considerably overestimates population risk for breast cancer incidence in Singapore'.

They said: "For patients, early detection adds to the increased risks of procedures such as breast biopsies as well as the risks of unnecessary treatment and medical expenses.

"Over-diagnosis also adds to patient anxiety and has social implications."

They said four out of five large studies in the world have found no improvement in survival when breast cancer was discovered at the pre-invasive stage, and even among "invasive cancers", one in three mammograms is non-threatening.

The study also found that women who had their first period before the age of 12, have had a breast biopsy and had their first child after age 30 were at higher risk.

Those who have never borne children are also generally at higher risk than those who have.

Dr Chay Wen Yee, the first author of the study, said: "These study findings mean that local doctors must place a greater emphasis on family history to accurately predict a woman's risk of breast cancer, and indeed, of any cancer.

"A carefully taken family history is a cheap, proven and easily available method to determine proper timing and intensity of cancer screening."

Salma Khalik
The Straits Times

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