Objective
To make recommendations about screening for breast cancer in asymptomatic women aged 40 to 49 years and 50 to 69 years in Canada.
Objective
To make recommendations about screening for breast cancer in asymptomatic
women aged 40 to 49 years and 50 to 69 years in Canada.
Burden of Suffering
Breast cancer is the third most common cause of death in women in Canada and excluding skin cancer is the most common cancer in women in Canada. There were an estimated 16,300 new cases of breast cancer in Canada in 1993 and an estimated 5,400 deaths. Over the last 20 years the incidence rate has increased by about 15% whereas the mortality has remained relatively stable.
Within Canada, there is an east-west gradient with lower rates in the
east. Risk factors for breast cancer include hormonal, dietary and hereditary
factors. Early menarche, late menopause and delayed first pregnancy are
associated with higher risk. There is some evidence linking high intake
of dietary fat to risk of breast cancer; family history, obesity, alcohol
use, ionizing radiation and post-menopausal estrogen replacement therapy
have also been associated with increased risk, while the evidence for oral
contraceptives is more controversial.
Options
Screening methods were clinical breast examination, mammography and
breast self-examination (BSE).
Outcomes
Main outcome was mortality, indicated by mortality or survival rates.
Other outcomes included factors associated with improved survival (stage,
tumour size, axillary node involvement). Sensitivity and specificity of
tests were also reported.
Evidence
Data sources included a MEDLINE search in November 1993 using the keywords
"breast neoplasms", "mass screening", "guideline", "familial or genetic
markers"; and a search of the author’s personal files.
Values
The 13-member Task Force of experts in family medicine, geriatric medicine,
pediatrics, psychiatry and epidemiology used an evidence-based method for
evaluating the effectiveness of preventive health care interventions. Recommendations
were not based on cost-effectiveness of options. Patient preferences were
not discussed.
Background papers providing critical appraisal of the evidence and tentative
recommendations prepared by the chapter author were pre-circulated to the
members. Evidence for this topic was presented and deliberated upon in
1- to 2-day meetings, 2 to 3 times per year from January 1993 to June 1993.
Consensus was reached on final recommendations.
Benefits, Harms, and Costs
Sensitivities and specificities for detection were 46% to 88% and 82%
to 99.9% respectively, and varied by screening method, screening interval
length, incidence of disease and method of calculating estimates of screening
proficiency. In a Canadian trial, the sensitivity of annual mammography
plus clinical examination (based on ratio of screen-detected cases to all
cases) was 88% in women aged 50 to 59 years and 81% in women 40 to 49 years.
Specificity (using surgical biopsy as gold standard) ranged from 96.5%
to 99.9%.
7 RCTs examined screening using clinical examination and/or mammography in women aged 40 to 74 years, randomized by individual or by neighbourhood or practice clusters. All found reductions in mortality in women over aged 50 – 69 years of age. None found significant benefits for women aged 40 to 49 years (relative risks ranged from 0.51 to 1.36).
5 studies reported an association between BSE and factors associated
with better survival (stage, tumour size, axillary node involvement); 2
found no benefit. Cohort studies suggest decreased mortality among women
who practice BSE, although these results may reflect lead-time, length-time
and self-selection biases.
Recommendations
Recommendation grade [A, B, C, D, E] and level of evidence
[I, II-1, II-2, II-3, III] are indicated after each recommendation. Citations
in support of individual recommendations are identified in the guideline
text.