The Canadian National Breast Screening Study-2
(CNBSS-2) published Thursday in the Journal of the National Cancer Institute
may be flawed because it is based on poor quality mammograms that were done
before the introduction of specific training and quality accreditation in
mammography and because of the basic design of the study. According to the Canadian Association of Radiologists (CAR), the CNBSS-2 falsely
concludes that adding mammography for breast cancer screening to physical
examinations does not reduce deaths.
The Canadian Association of Radiologists (CAR) is leveling this strong
criticism at the study is pointing out that the authors used the same flawed
methods in following women 50-59 as they did in a previously published and
highly criticized study of women 40-49.
The CAR is firmly rejecting the study's conclusions and is urging women
to continue to have regular mammography screening, starting at age 40. The
Canadian Cancer Society's Annual Report clearly shows that the decline in the
breast cancer death rate of the past decade is directly associated with the
introduction of mammography screening programs in Canada. ``It would be tragic
if women were persuaded not to have screening mammography based on the highly
questionable results of this latest CNBSS Study-2'' said Dr. John W. Radomsky,
President of the CAR. ``Other, well conducted, screening trials have
documented that mammography does indeed save lives.''
In addition to major quality issues, the study design involving
volunteers, can not be used to draw conclusions about the general population.
The authors correctly point out that the death rate in their control group is
far lower than in the average Canadian population.
This was also true in their previously published study of women ages
40-49, where the control group did not have repetitive screening. Their
greater than 90% five year survival among women ages 40-49 strongly suggests a
In the newly released study of women 50-59, the extremely small
percentage of lymph node positive cancers (13%) among women receiving only the
Clinical Breast Examination (CBE) is unheard of in any other study raising
additional concerns about the allocation of patients in the study groups. The
extremely low mortality rate of 105/610 (17%) at 10 years among this same
group of women is also unprecedented.
The most recent data confirm the poor quality of mammography screening in
the NBSS-2. In virtually every other comparison of palpable mammography
detected cancers done since the introduction of the quality control program,
the majority of cancers are detected by mammography alone. Most are non-
palpable, even in retrospect.
In NBSS-2, almost as many cancers are detected by clinical examination
alone as by mammography and clinical breast examination, although there were
more cancers expected from high quality mammography.
What needs to be understood by those who will read these results is that
in the early 1980s, at the time the study was conducted, mammography screening
was not commonly being performed and specific training for radiologists not
In the 1990s the CAR introduced an Accreditation Program to certify the
centres offering high quality mammography as well as specific training for
radiologists in quality control and management. Today, 76% of all mammography
units are enrolled into the CAR Accreditation Program. Women are invited to
consult the CAR website to identify the centres they should go to for their
In addition to strongly criticizing this study, the CAR questioned why
offers of support by skilled radiologists in the 80s were turned down and why
the Journal of the NCI published such a controversial paper without an
Vidyya reported on the original findings of the study on 21 September 2000. You can read a summary in our archives.