Mammography Screening: To Screen or Not to Screen?
Recently, the Swiss Medical Board proposed discontinuing
screening of women for breast cancer using mammography. The report did not
suggest an alternate. The board included a medical ethicist, a clinical
epidemiologist, a clinical pharma-cologist, an oncologic surgeon, a nurse
scientist, a lawyer and a health economist. Two of the board, the ethicist and
epidemiologist, have written about the report, pointing out four particular
concerns they had (none of the four argued for screening). In both this and the
next blog, I want to quote extensively from their report (the entire report and
the text from the two members are available) (1,2).
The first point addressed the fact “that the ongoing debate
[over screening with mammograms] was based on a series of re-analyses of the
same, predominantly outdated trials. The first trial started more than 50 years
ago in New York City and the last trial in 1991 in the United Kingdom. None of
these trials were initiated in the era of modern breast-cancer treatment, which
has dramatically improved the prognosis of women with breast cancer.”
In 2011, a study from the UK showed an increasing
effectiveness -- from a 28% reduction in breast cancer mortality in the period
1975-1991 to 65% in the period 1992-2008. The article did not report on the
mortality in the population at large (3). It was this that led to the second
issue the board raised – “over diagnosis.” The two members of the board said
that they “were struck by how non-obvious it was that the benefits of
mammography screening outweighed the harms. The relative risk reduction of
approximately 20% in breast-cancer mortality associated with mammography that
is currently described by most expert panels came at the price of a
considerable diagnostic cascade, with repeat mammography, subsequent biopsies
and over diagnosis of breast cancers — cancers that would never have become
clinically apparent. The recently published extended follow-up of the Canadian
National Breast Screening Study is likely to provide reliable estimates of the
extent of over-diagnosis. chemotherapy or some combination of these therapies.”
In my next blog, I will discuss the third and fourth
comments that the ethicist and epidemiologist brought to our attention.
1. N Engl J
Med. 2014 Apr 16.
3. Br J
Cancer. 2011 Mar 15;104(6):910-4.