Breast Cancer Screening: Why Can't Experts Agree?
But last week, a new study published in the British Medical Journal found that screening large numbers of women for breast cancer failed to significantly reduce deaths from the disease in Danish women. This contrasts with earlier findings, specifically one that found a 25% reduction in breast cancer mortality in Copenhagen following the introduction of mammography screening.
No Benefit From Wider Screening?
What's more, the study found even less reduction in mortality in the two areas of Denmark that offered public breast cancer screening programs than in the rest of the country during the 1997-2006 study period.
For example, in women ages 55 to 74, who could benefit most from screening, the researchers found a mortality decline of 1% a year in the screening areas. Yet, in women of the same age in the nonscreening areas (which cover 80% of the population), there was a mortality decline of 2% a year.
Similarly, in younger women -- ages 35 to 55 years -- breast cancer mortality declined 5% a year in the screening areas and 6% a year in the areas that didn't offer public mammography screening programs.
To explain the contradiction with the earlier study, the researchers at the Nordic Cochrane Centre in Copenhagen and the Norwegian Institute of Public Health in Oslo say the previous study had some design flaws, including exclusion of some groups and areas and an incorrect time line. They believe that changes in risk factors and improvements in treatment, such as the use of AstraZeneca's (AZN) Nolvadex, generically known as tamoxifen, were probably the reason for the reduced mortality rather than the screening program.
Time to Question Results
While the authors of the trial agree that observational studies such as theirs are problematic, they say that results of similar studies in other countries such as Sweden, the U.K. and the U.S. support their findings.
"We believe it is time to question whether screening has delivered the promised effect on breast cancer mortality," they conclude.
If there was uproar and confusion in November following the Preventive Task Force proposal to scale back mammography screening, this new study is bound to stir the pot further.
It's important first to note that the effectiveness of mammography as a diagnostic tool -- to check a lump or abnormality -- is not in question here. What's in question here are the massive screening programs many governments have initiated to try to combat the most common cancer in women worldwide.
Another important point to note is that the screening program guidelines are not for higher-risk women. Last, the study doesn't necessarily say screening is worthless, but that the benefits of large-scale screening programs may be oversold.
Pros and Cons
So why can't researchers, doctors and experts around the world agree?
Looking at some of the research out there, it gets confusing. Different studies support different views, with researchers often attacking methods of one study or another. For example, Dr. Cornelia J. Baines, professor emerita at the Dalla Lana School of Public Health at the University of Toronto, wrote in the Globe and Mail in favor of the study, pointing to other similar studies regarding cervical cancer screening that affected public policy and lowered cervical cancer deaths considerably.
But other researchers and patient advocacy groups point out the limitations of observational studies such as the Danish one. Properly randomized studies have shown considerable reduction in mortality, they say. Further, the findings from Denmark aren't necessarily applicable to other countries, as Heather Chappell, director of the Canadian Cancer Society, writes. Robert Smith, director of cancer screening at the American Cancer Society (ACS), also criticized the study, saying it covered only a short period of time.
General Electric's (GE) GE Healthcare, Hologic (HOLX) and Siemens (SI) are three companies at the forefront of improving the screening technology.
The ACS says mammography reduces breast cancer mortality in women ages 40 to 74 and recommends yearly mammograms for women starting at the age of 40. European and Canadian guidelines usually recommend screening starting at 50.
The effectiveness of mammography as a diagnostic tool isn't in question, as is the fact that it's not without risks. The National Cancer Institute says the risks of breast cancer screening include:
- Finding breast cancer may not improve health or help a woman live longer. The reason: Not all cancers are life-threatening, but doctors don't know which is which and treat all cancers found. The treatment -- from surgery to radiation to chemotherapy -- can cause serious side effects. Indeed, the Danish study found that the incidence of ductal carcinoma in situ -- a noninvasive growth in a milk duct that sometimes progresses to breast cancer -- doubled in the screened areas, but remained flat in the nonscreened areas.
- False-negative test results can occur -- showing there is no cancer when there really is.
- False-positive test results can occur -- showing there is cancer when there really isn't. Anxiety and more unnecessary tests are just some of the consequences.
- Mammograms expose the breast to radiation.
Moreover, critics say massive screening programs eat up hospital and manpower time and costs, without preventing enough deaths to justify those resources.
For women who feel their lives have been saved because of a regular screening there is no question of its value. If one life is saved for every 1,000 or 2,000 tests, screening is worthwhile. For doctors who feel the same, there's also no question of the usefulness of the tests.
Conversely, some doctors feel they treat women for cancer who may not have needed to be if it weren't for the screening. But with such an emotionally charged issue, it's hard to determine what's the best policy.
The answer may be somewhere in the middle. While breast cancer screening can definitely save lives, the benefits may be far less than what some proponents claim. The decision is ultimately an individual one, and women should consult their doctors and be as informed as they can.