Please note: In 2003, the CTF updated its Grades of Recommendations to include an "I Recommendation" for situations where insufficient evidence exists to allow a recommendation to be made.  (Formerly, these situations were captured under a "C Recommendation".)  This change is not retroactive, and all "C Recommendations" made prior to 2003 have not been reevaluated in light of the new "I" recommendation grade.  For a discussion of these recommendation grades, please link to the 2003 article in the Canadian Medical Association Journal here.

Preventive Health Care, 2001 update: Screening
mammography among women aged 40–49 years at average risk of breast cancer

Structured Abstract

Prepared by Jolie Ringash, MD, MSc, FRCP(C), Princess Margaret Hospital-University Health Network/University of Toronto, Ontario

These recommendations were finalized by the Task Force in August 1999

Objective
This review considers new and updated evidence regarding the effect of screening mammography on breast cancer mortality among women aged 40-49 at average risk of breast cancer.  A previous review by the Canadian Task Force on the Periodic Health Examination (now the Canadian Task Force on Preventive Health Care) in 1994 indicated fair evidence to exclude mammographic breast cancer screening of women aged 40-49 from the periodic health examination.

Burden of Suffering
Breast cancer is the most commonly diagnosed cancer in Canadian women, with an estimated 18,700 new cases and 5,400 deaths in 1999.  For women at average risk, secondary prevention (early detection) may reduce breast cancer mortality.  Randomized controlled trials (RCTs) have shown that screening mammography reduces mortality among women aged 50-70.  Currently, Canadian women under 50 are not recruited for breast cancer screening, but they are accepted for screening in 7 of 11 Canadian regions.  

Options
Screening mammography starting at either age 40 or age 50.

Outcomes
Reduction in breast cancer mortality.

Evidence
The MEDLINE and CANCERLIT databases were searched for relevant articles published from 1966 to January 2000. Of 68 references obtained, at least 22 were published after the 1994 review. To date, the only trial designed to assess the mortality benefits of screening mammography among women aged 40–49 did not have adequate power to exclude a clinically significant benefit. Other results from randomized controlled trials (RCTs) are post-hoc subgroup analyses of larger trials.

Recommendations were graded as:

Quality of evidence was rated according to 5 levels:

I	Evidence from at least 1 properly randomized controlled trial (RCT).
II-1	Evidence from well-designed controlled trials without randomization.
II-2	Evidence from well-designed cohort or case-control analytic studies, preferably from more than 1 centre or research group.
II-3	Evidence from comparisons between times or places with or without the intervention. Dramatic results in uncontrolled experiments could also be included here.
III	Opinions of respected authorities, based on clinical experience, descriptive studies or reports of expert committees.

Values
The 13-member Task Force of experts in family medicine, geriatric medicine, paediatrics, 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 a 2-day meeting in May 1998.  Consensus was reached on final recommendations.

Benefits, Harms, and Costs
Screening mammography offers the potential for significant benefits in addition to mortality reduction, including early diagnosis, less aggressive therapy and improved
cosmetic results. However, the risks of screening include increased biopsy rates and the psychological effects of false reassurance or false-positive results. Although several of the trials reviewed constitute level I evidence (RCT), at present their conflicting results, methodologic differences and, most important, uncertainty about the risk:benefit ratio of screening precludes the assignment of a "good" or "fair" rating
to recommendations drawn from them.  Cost-effectiveness was not evaluated.

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.

• Current evidence regarding the effectiveness of screening mammography does not suggest the inclusion of the manoeuvre in, or its exclusion from, the periodic health examination of women aged 40–49 years at average risk of breast cancer [C, I]. Upon reaching the age of 40, Canadian women should be informed of the potential benefits and risks of screening mammography and assisted in deciding at what age they wish to initiate the manoeuvre. 

Validation
The members of the Canadian Task Force on Preventive Health Care reviewed the findings of this analysis through an iterative process. The task force sent the final review and recommendations to three selected external expert reviewers, and their feedback was incorporated. It was then peer-reviewed as part of the journal publication process.

Sponsors
The Canadian Task Force on Preventive Health Care is funded through a partnership between the Provincial and Territorial Ministries of Health and Health Canada.

Selected References

Ringash, J. with the Canadian Task Force on Preventive Health Care. Preventive health care, 2001 update: screening mammography among women aged 40-49 years at average risk of breast cancer. CMAJ 2001; 164(4):469-76.