Breast cancer biology 'changing'

Lifestyle changes and screening haveshifted the type of breast cancers women are diagnosed with over thepast couple of decades, research suggests.

Women are now more likely to have hormone-dependent,slow-growing tumours, a comparison of tissue samples from the 1980s and1990s shows.

The Scottish researchers also found improved survival over time, the British Journal of Cancer reported.

More than 40,000 women are diagnosed with breast cancer in the UK annually.

Previous studies have suggested that breast cancers may be more commonly hormone-dependent than in the past.

It's plausible that lifestyle changes could be influencing the types of breast cancers that women are developing but we will need much larger studies to find out whether this trend is real
Dr Alison Ross, Cancer Research UK

Specifically it is thought that oestrogen-receptor positive cancers may be on the rise.

It is these tumours which respond well to hormone therapy, such as tamoxifen which prevents the disease coming back.

But it has not been clear that numbers were actually on the riseas the ability to detect these types of tumours in the lab may haveimproved in recent years.

In the latest study, researchers re-examined actual tissuesamples - 420 from between 1984 and 1986 and 653 from 1996 to 1997 -saved by two large hospitals in Glasgow.

Those diagnosed in the earlier time period had all presentedwith symptoms of cancer because screening by mammography had not yetbeen introduced.

The proportion of cancers which were oestrogen-receptorpositive changed significantly from 64.2% to 71.5% over the 10-yearperiod.

And more cancers were diagnosed as grade one - slow-growingtumours, with a decline in the number of grade three - fast-growingtumours.

There was no change over time in the proportion of progesterone or Her-2 positive cancers

Lifestyle

It could be that screening is detecting more oestrogen-receptorpositive cancers because they are slow-growing and may be detectedbefore symptoms appear.

But another explanation could be changes in lifestyle factorswhich increase the risk of hormone-dependent tumours, such as womenhaving babies at an older age, obesity after menopause and use ofhormone replacement therapy.

The researchers, led by Dr Sylvia Brown at Crosshouse Hospitalin Ayrshire wrote: "There is evidence that the percentage of allchildren being born to mothers aged 35 years and over is increasing inScotland and that means BMI and prevalence of obesity are increasing."

She added that if there is a true increase in the proportion ofthese tumours it has implications for treatment decisions as manyclinical trials were carried out in previous decades.

Dr Alison Ross, Cancer Research UK's senior science informationofficer, said: "It's plausible that lifestyle changes could beinfluencing the types of breast cancers that women are developing butwe will need much larger studies to find out whether this trend isreal.

"And it's also not clear whether these results reflect a shiftin breast cancer biology or indicate that screening is better atdetecting certain cancers.