Biology of Breast Cancer is Changing
Research suggests that lifestyle changes and screening have shifted the type of breast cancers women are diagnosed with over the past couple of decades.
It is now considered that women will more likely have hormone-dependent, slow-growing tumors, a comparison of tissue samples from the 1980s and 1990s shows.
The British Journal of Cancer reported, that Scottish researchers also found improved survival over time. Over 40,000 women are diagnosed with breast cancer in the U.K. annually, and almost 200,000 in the U.S.
In the past, studies have suggested that breast cancers might be more commonly hormone-dependent than before. It is thought specifically that oestrogen-receptor positive cancers might be on the rise.
These tumors respond well to hormone therapy, like tamoxifen, which prevents the disease coming back.
However, it is not clear that numbers were actually on the rise as the ability to detect these types of tumors in the lab may have improved in recent years.
Researchers re-examined actual tissue samples in the last study, which were saved by two large hospitals in Glasgow.
The ones diagnosed between 1984 and 1986 had all presented with symptoms of cancer because screening by mammography had not yet been introduced.
The proportion of cancers that were oestrogen-receptor positive changed drastically from 64.2% to 71.5% during the 10-year period.
Also, more cancers were diagnosed as grade one fast-growing tumors.
There was not a change over time in the proportion of progesterone or Her-2 positive cancers.
This might be because screening is detecting more oestrogen-receptor positive cancers due to them being slow-growing and may be detected before symptoms appear.
Another explanation might be changes in lifestyle factors which increase the risk of hormone-dependent tumors, like women having babies at an older age, obesity after menopause and use of hormone replacement therapy.
The researchers, led by Dr Sylvia Brown at Crosshouse Hospital in Ayrshire wrote, “There is evidence that the percentage of all children being born to mothers aged 35 years and over is increasing in Scotland and that means BMI and prevalence of obesity are increasing.”
If there is a true increase in the proportion of these tumors it has implications for treatment decisions as many clinical trials were carried out in previous decades, she added.
Cancer Research U.K.’s senior science information officer, Dr. Alison Ross, said, “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.”
“And it’s also not clear whether these results reflect a shift in breast cancer biology or indicate that screening is better at detecting certain cancers,” she added.
“If the trend identified in this interesting study is confirmed and continues, it could have an impact on the way doctors apply results from breast cancer studies done decades ago to the treatments in use today.”
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