Mammograms are a
mixed bag
Too much money is wasted on unnecessary breast cancer
screenings.
It is always better to find
cancer early by screening, right? Well actually, it depends. For some cancers
(e.g. colon cancer) the evidence is clear: screening saves lives. For other
cancers like breast cancer, the answer is a contentious, mixed bag
This is not a purely academic
question – U.S. mammogram screening for breast cancer costs $8 billion per year. A new study in JAMA
Internal Medicine suggests this is not money well spent. Current screening
programs recommending annual mammograms starting at age 40 may harm some of the
women they are meant to help and waste billions of dollars.
If screening is effective, it
should pick up cancers early to reduce the number of cancers diagnosed at an
advanced stage (i.e., those most likely to kill) and decrease breast cancer
mortality. The study compared different rates of screening, breast cancer
incidence and breast cancer mortality in 16 million women 40 years old and
older, residing in 547 U.S. counties. The women were screened for breast cancer
in 2000 and followed for 10 years.
The study found a positive
correlation between the extent of screening and breast cancer incidence, i.e.,
more screening finds more cancers. But there was no correlation between the
extent of screening and 10-year breast cancer mortality. The increased numbers
of cancers discovered by screening were largely small cancers (less than 2
centimeters) and early stage cancers. There was neither a reduction in the
numbers of larger cancers, nor in the incidence of more dangerous cancers
whether locally advanced or that had already spread through distant metastases.
These new findings mirror a 2012
New England Journal of Medicine review of
30 years of mammography screening that
showed a 109
percent increase in the incidence of small, early-stage breast cancer but only
an 8 percent decrease in the incidence of advanced cancers with virtually no
reduction in the most advanced, metastatic cases.
Why hasn’t screening delivered? A
big part of the problem is overdiagnosis: finding early forms of cancer such as
non-invasive disease or very early invasive disease that would have never
become clinically apparent or affected the woman’s life expectancy. An
estimated 19-31 percent of mammographically detected cancers are over-diagnosed.
Once uncovered, these cancers are treated with surgery (with young women
increasingly selecting unilateral or even bilateral mastectomies rather than
lumpectomies), radiation (which can affect the heart and lungs), and toxic
chemotherapy – all of which is unnecessary. The women are left psychologically
traumatized by the inaccurate diagnosis of a life threatening disease.
Overdiagnosis is not the only
problem with screening. 20 percent of patients screened with mammography are
told something is wrong when in fact nothing is wrong. These “false positives”
lead to additional testing, unneeded biopsies and anxiety until the diagnostic
uncertainty is resolved. A study in the health policy journal Health Affairs
finds that overdiagnosis and false positives in women 40-59 years old costs $4
billion per year – i.e., half of the annual expenditure on mammography
screening. There is also a 20 percent rate of mammograms missing cancers that
are actually there. These “false negatives” give women a false sense of
reassurance and may lead them, and sometimes their physicians, to ignore signs
and symptoms of disease like a breast mass.
None of the above is meant to
suggest that screening should never be done, only that it should be directed at
the people most likely to benefit. The ability of mammography to uncover
dangerous breast cancers rises as women age because the incidence of breast
cancer rises and the breasts become less dense, making mammograms easier to
interpret. The number of screening harms declines as women age for the same
reasons.
The U.S. Preventive Services Task
Force recently released updated recommendations for breast cancer screening and found that
for
women under age 50 who have an average risk of cancer, the harms outweigh the
benefits of screening. It recommends that women between the ages of 50-74
should be screened only every other year, and suggests that women below 50
consult with their physicians to discuss if their history and individual risk
factors warrant screening before age 50. The American College of Physicians
High Value Care Task Force recently made identical recommendations. These
recommendations mirror guidelines used around the world. The U.S. has been
unique in initiating annual screening at age 40 and continuing indefinitely (50
percent of women over 80 are screened despite the Preventive Services Task
Force’s recommendation to stop at 74). Other countries start at 50 and then
test every two to three years up to 70-74 years old.
Raising the starting age and
decreasing the frequency of screening programs has been loudly criticized by a
variety of patient and cancer advocacy groups. Politicians have also chimed in.
Rep. Debbie Wasserman Schultz, D-Fla., who was diagnosed with breast cancer at
age 41, warned in the Washington Post that,
“deferring them [mammograms] until after age 50 is dangerous” and will result
in “needless deaths.” But her criticism fails to take into account the
documented limitations and pitfalls of mammography. Ironically, Wasserman Schultz
discovered the lump in her breast herself, two months after a negative
screening. Thankfully, she was aware of the signs of breast cancer and was not
falsely reassured by the false negative mammogram..
Screening early and often, no
matter how well intentioned, is costly and counterproductive. Finding every
last cancer, no matter how small or innocuous, does not save lives and subjects
many women to unnecessary treatment. If we are serious about evidence-based
medicine and greater value in healthcare, mammogram screening should be limited
to those populations most likely to benefit. The money saved would be better
spent on breast cancer research and treatment and on providing women with the
information they need to make informed decisions about cancer screening.
