Breast cancer screening has not played a direct part in the reductions of breast cancer mortality in recent years, says a new study published on bmj.com.
An international team of researchers from France, the UK and Norway found that improving health systems are more likely to have led to falling numbers of deaths from breast cancer than screening.
Breast cancer screening with mammography protocols actually results in an increase in breast cancer mortality, according to long-term follow-ups in large-scale studies.
In a Swedish study of 60,000 women, 70 percent of the mammographically detected tumors weren't tumors at all. These "false positives" aren't just financial and emotional strains, they may also lead to many unnecessary and invasive biopsies. In fact, 70 to 80 percent of all positive mammograms do not, upon biopsy, show any presence of cancer.
At the same time, mammograms also have a high rate of missed tumors, or "false negatives." Dr. Samuel S. Epstein, in his book, The Politics Of Cancer, claims that in women ages 40 to 49, one in four instances of cancer is missed at each mammography. The National Cancer Institute (NCI) puts the false negative rate even higher at 40 percent among women ages 40-49. National Institutes of Health spokespeople also admit that mammograms miss 10 percent of malignant tumors in women over 50. Researchers have found that breast tissue is denser among younger women, making it difficult to detect tumors. For this reason, false negatives are twice as likely to occur in premenopausal mammograms.
Radiation exposure in known to cause genetic mutation in breast cells. It is also known to switch off the tumour suppressing gene. Now, new research from the Lawrence Berkeley National Laboratory in America (a US Government facility) has shown that radiation both changes the environment around breast cells, and increases the risks of mutation within them; a mutation that can be passed on in cell division.
This study showed that 4 to 6 weeks after exposure to radiation at a level below that of a screening mammogram, breast cells started to prematurely age. This resulted in their inability to send certain chemical messages into their immediate environment, which then filled with pre-cancerous mutated cells also from the radiation.
"Our work shows that radiation can change the microenvironment of breast cells, and this in turn can allow the growth of abnormal cells with a long-lived phenotype that have a much greater potential to be cancerous," said Paul Yaswen, a cell biologist and breast cancer research specialist with Berkeley Lab´s Life Sciences Division, adding "Many in the cancer research community, especially radiobiologists, have been slow to acknowledge and incorporate in their work the idea that cells in human tissues are not independent entities, but are highly communicative with each other and with their microenvironment."
The number of deaths from breast cancer is falling in many developed countries, but it is difficult to determine how much of that reduction over the past 20 years of mammography screening is due to earlier detection or to improved management.
From 1965 to 1980, cervical cancer mortality fell earlier and more strongly in Nordic countries that implemented nationwide screening programmes compared with those that delayed screening.
So the team used a similar approach to compare trends in breast cancer mortality within three pairs of European countries – Northern Ireland versus Republic of Ireland, the Netherlands versus Belgium and Flanders, and Sweden versus Norway.
The researchers expected that a reduction in breast cancer mortality would appear sooner in countries with earlier implementation of screening.
Countries of each pair had similar healthcare services and level of risk factors for breast cancer mortality, but were different in that mammography screening was implemented about 10 to 15 years later in the second country of each pair.
The researchers studied data from the World Health Organisation (WHO) mortality database on cause of death covering the period 1980 to 2006 and data sources on risk factors for breast cancer death, mammography screening, and cancer treatment.
Results showed that from 1989 to 2006, deaths from breast cancer fell by 29% in Northern Ireland and 26% in the Republic of Ireland; by 25% in the Netherlands, 20% in Belgium and 25% in Flanders; and by 16% in Sweden and 24% in Norway.
These trends in breast cancer mortality rates varied little between countries where women had been screened by mammography for a considerable time compared with those where women were largely unscreened during that same period, say the authors. Furthermore, the greatest reductions were in women aged 40-49, regardless of the availability of screening in this age group.
They conclude: "The contrast between the time differences in implementation of mammography screening and the similarity in reductions in mortality between the country pairs suggest that screening did not play a direct part in the reductions in breast cancer mortality."