Screening may be another factor in the changing histological types of breastcancer. Scottish researchers, reporting in the British Journal of Cancer, say that women are now more likely to have hormone-dependent, slow growing tumours than they were in the 1980s and 1990s.
Researchers have used a comparison of tissue samples from the past two decades.
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
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 rise as the ability to detect these types of tumours in the lab may have improved in recent years.
In the latest study, researchers re-examined actual tissue samples - 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 presented with symptoms of cancer because screening by mammography had not yet been introduced.
The proportion of cancers which were oestrogen-receptor positive changed significantly from 64.2% to 71.5% over the 10-year period.
And more cancers were diagnosed as grade one - slow-growing tumours, with a decline in the number of grade three - fast-growing tumours.
There was no change over time in the proportion of progesterone or Her-2 positive cancers.
The authors say that these changes may be bacause screening is now detecting slow growing cancers, which are more likely to be hormone dependent. But they also suggest that lifestyle changes such as delaying childbirth, obesity and use of hormone replacement therapy may be playing a part.
