Data discount benefit of mammograms

[Guest guest]

http://www.medicalpost.com/mdlink/english/members/medpost/data/3831/01A.HTM

 

 

Data discount benefit of mammograms

 

Study of women ages 40 to 49 showed similar death rates with or

without screening

By David Hodges

 

TORONTO - Mammography screening does not reduce breast cancer

mortality in women age 40 to 49 years, according to findings from the

Canadian National Breast Screening Study-1 (CNBSS-1).

After 13 years of followup, results of the major study showed that

women receiving annual mammography had similar death rates to those who did

not receive the intervention.

The results will likely cause a great deal of debate among breast

cancer experts and radiologists. Two years ago, 13-year followup results

from the CNBSS-2 were met with a storm of controversy after findings

demonstrated that mammography offered no reduction in breast cancer deaths

among women ages 50 to 59.

" This study is as straightforward as it ever has been, but it is

absolutely unacceptable to the screening industry, " said lead investigator

Dr. Cornelia Baines, a professor in the department of public health sciences

at the University of Toronto and medical consultant for the Medical Post.

In particular, Dr. Baines referred to the controversial question of

whether mammography screening leads to " overdiagnosis " of breast cancer-that

is, the detection of a tumour that would not have become clinically

detectable in the patient's lifetime.

The CNBSS-1 data suggest overdiagnosis of nonpalpable or

insignificant invasive breast tumours may occur. This is based on the fact

that although more breast cancers were detected with mammography in their

study, this did not improve breast cancer mortality.

The study randomly assigned 50,430 women ages 40 to 49 years to

receive either screening with annual mammography, breast physical

examination and instruction on breast self-examination on four or five

occasions; or usual community care after a single breast physical

examination and instruction on breast self- examination.

The women were recruited from January 1980 to March 1985 across 15

Canadian centres. Eligible women in the study were not pregnant, had no

previous breast cancer diagnosis, and had not had mammography in the

preceding 12 months.

After 11 to 16 years of followup, results showed 105 breast cancer

deaths in the mammography group and 108 breast cancer deaths in the usual

care group. A total of 592 cases of invasive breast cancer and 71 cases of

in situ breast cancer were diagnosed by Dec. 31, 1998, in the mammography

group compared with 552 and 29 cases, respectively, in the usual care group.

The CNBSS-1 results showed that unless the lead time gained by

mammography exceeded 10 years, an excess 40 cases of invasive breast cancer

detected by mammography persisted. This represented 58% of non-palpable

invasive breast cancer and 70% of the non-palpable tumours in the

mammography group. This proportion is greater than 50% of cases of in situ

plus invasive cancer detected by screening in the mammography group that

meet the definition of minimal breast cancer (in situ plus invasive tumours

less than 10 mm in diameter), according to the study.

For women younger than 50 years of age, the benefits of screening

mammography are uncertain, Dr. Baines and colleagues concluded. Women must

also consider the adverse consequences of false-positive mammograms, they

added.