The denser the breast tissue, the greater the risk of breast cancer
By Sheryl Ubelacker
TORONTO (CP) - Women with a high proportion of dense tissue in their breasts have a far greater risk of developing breast cancer than women with low-density tissue, a long-term Canadian study has found.
The study analyzed mammograms from three large screening programs in Canada, comparing those of more than 1,100 women who developed breast cancer after their baseline X-ray with an equal number of women who did not get the disease. The researchers followed the women's mammography history for eight years.
"We found that the amount of density in the breast was very strongly related to the risk of breast cancer subsequently and that people with density in more than 75 per cent of their breast, compared to those with less than 10 per cent, had a five-fold elevation in breast cancer risk," said principal researcher Dr. Norman Boyd.
"And this persisted after taking into account all other (risk) factors," including a family history of breast cancer, number of children, and age of onset of menstruation and menopause, said Boyd, a senior scientist at Toronto's Princess Margaret Hospital.
"This study establishes that breast density is an extremely important risk factor for developing breast cancer," he said. "Depending on a woman's age, between 16 and 30 per cent of breast cancers can be attributed to extensive density."
"Other risk factors, including family history and the known genes, account for a much smaller proportion of the disease."
In the study, published Thursday in the New England Journal of Medicine, breast density varied among the women from less than 10 per cent to more than 75 per cent of tissue. About five to 10 per cent of subjects had the highest density measurement.
On mammograms, fat looks dark, but the denser milk-duct and connective tissues in breasts show up as light patches. "What we're referring to as density is what we see as white on the mammogram," Boyd said Wednesday, noting that whether a women has large or small breasts has no bearing on density.
The problem with dense tissue is that it can mask the presence of tumours, which also appear white. But this study confirms that cancers are actually more frequent - not just hidden - in women with dense breasts.
While having dense breasts does not inevitably lead to a future diagnosis of breast cancer - "which is very far from being the case " - women should consider it as one more factor when tallying their personal risk of developing cancer and be vigilant about regular examination and screening, he advised.
Doctors, too, should be more aware of the potential risk for breast cancer, the second deadliest kind for women after lung cancer. More than 22,000 Canadians were diagnosed last year with breast cancer, which killed about 5,300 women.
"At the moment, the screening programs everywhere take a standard approach to all women regardless of the type of tissue they have in their breast. And it may be that they should be thinking more in terms of tailoring the intervals between screening and perhaps the methods that they use for screening according to those characteristics."
Women with little or no density might be seen less often, while those with higher density might be seen more frequently and given additional, more sensitive diagnostic tests such as ultrasound, MRI or computerized mammograms, he added.
While some doctors agree that the more sophisticated tests might be better at detecting tumours in very dense breasts, the cost could be prohibitive - especially in the case of magnetic resonance imaging (MRI) machines, which have limited availability across Canada.
"In a perfect world, I would have my wife do an ultrasound, MRI and a digital mammogram," Dr. Gary Whitman told The Associated Press. The radiologist from the University of Texas M.D. Anderson Cancer Center was not involved in the study.
Commenting on the research in an editorial, Dr. Karla Kerlikowske of the University of California at San Francisco said routine mammography that includes a measurement of breast density could help doctors estimate breast cancer risk.
"The time has come to acknowledge breast density as a major risk factor for breast cancer and to determine, develop and test the best ways to measure breast density in clinical practice and use this measurement to maximize primary and secondary prevention of breast cancer," Kerlikowske writes.
The idea that breast density is linked to an elevated risk of breast cancer has been around for several decades, but the Canadian study is the largest to date based on modern mammography. It also is the first to use special computer-assisted technology to measure density, which allowed the scientists "to assess the effects of this phenomenon referred to as masking, because density makes cancer more difficult to detect," Boyd said.
"There's been persisting concerns up till now in some people's minds as to whether this masking phenomenon was somehow creating the appearance of risk when there actually wasn't any. And our study was designed in part to address that question."
"The conclusion we reached, of course, is that although there is some masking of cancer by density, that is not creating a spurious illusion of risk. There is a real, large underlying risk despite masking."
By Sheryl Ubelacker
TORONTO (CP) - Women with a high proportion of dense tissue in their breasts have a far greater risk of developing breast cancer than women with low-density tissue, a long-term Canadian study has found.
The study analyzed mammograms from three large screening programs in Canada, comparing those of more than 1,100 women who developed breast cancer after their baseline X-ray with an equal number of women who did not get the disease. The researchers followed the women's mammography history for eight years.
"We found that the amount of density in the breast was very strongly related to the risk of breast cancer subsequently and that people with density in more than 75 per cent of their breast, compared to those with less than 10 per cent, had a five-fold elevation in breast cancer risk," said principal researcher Dr. Norman Boyd.
"And this persisted after taking into account all other (risk) factors," including a family history of breast cancer, number of children, and age of onset of menstruation and menopause, said Boyd, a senior scientist at Toronto's Princess Margaret Hospital.
"This study establishes that breast density is an extremely important risk factor for developing breast cancer," he said. "Depending on a woman's age, between 16 and 30 per cent of breast cancers can be attributed to extensive density."
"Other risk factors, including family history and the known genes, account for a much smaller proportion of the disease."
In the study, published Thursday in the New England Journal of Medicine, breast density varied among the women from less than 10 per cent to more than 75 per cent of tissue. About five to 10 per cent of subjects had the highest density measurement.
On mammograms, fat looks dark, but the denser milk-duct and connective tissues in breasts show up as light patches. "What we're referring to as density is what we see as white on the mammogram," Boyd said Wednesday, noting that whether a women has large or small breasts has no bearing on density.
The problem with dense tissue is that it can mask the presence of tumours, which also appear white. But this study confirms that cancers are actually more frequent - not just hidden - in women with dense breasts.
While having dense breasts does not inevitably lead to a future diagnosis of breast cancer - "which is very far from being the case " - women should consider it as one more factor when tallying their personal risk of developing cancer and be vigilant about regular examination and screening, he advised.
Doctors, too, should be more aware of the potential risk for breast cancer, the second deadliest kind for women after lung cancer. More than 22,000 Canadians were diagnosed last year with breast cancer, which killed about 5,300 women.
"At the moment, the screening programs everywhere take a standard approach to all women regardless of the type of tissue they have in their breast. And it may be that they should be thinking more in terms of tailoring the intervals between screening and perhaps the methods that they use for screening according to those characteristics."
Women with little or no density might be seen less often, while those with higher density might be seen more frequently and given additional, more sensitive diagnostic tests such as ultrasound, MRI or computerized mammograms, he added.
While some doctors agree that the more sophisticated tests might be better at detecting tumours in very dense breasts, the cost could be prohibitive - especially in the case of magnetic resonance imaging (MRI) machines, which have limited availability across Canada.
"In a perfect world, I would have my wife do an ultrasound, MRI and a digital mammogram," Dr. Gary Whitman told The Associated Press. The radiologist from the University of Texas M.D. Anderson Cancer Center was not involved in the study.
Commenting on the research in an editorial, Dr. Karla Kerlikowske of the University of California at San Francisco said routine mammography that includes a measurement of breast density could help doctors estimate breast cancer risk.
"The time has come to acknowledge breast density as a major risk factor for breast cancer and to determine, develop and test the best ways to measure breast density in clinical practice and use this measurement to maximize primary and secondary prevention of breast cancer," Kerlikowske writes.
The idea that breast density is linked to an elevated risk of breast cancer has been around for several decades, but the Canadian study is the largest to date based on modern mammography. It also is the first to use special computer-assisted technology to measure density, which allowed the scientists "to assess the effects of this phenomenon referred to as masking, because density makes cancer more difficult to detect," Boyd said.
"There's been persisting concerns up till now in some people's minds as to whether this masking phenomenon was somehow creating the appearance of risk when there actually wasn't any. And our study was designed in part to address that question."
"The conclusion we reached, of course, is that although there is some masking of cancer by density, that is not creating a spurious illusion of risk. There is a real, large underlying risk despite masking."
