Cochrane for Clinicians

Putting Evidence into Practice

Counseling Women About Mammography: Benefits vs. Harms

MICHAEL B. POTTER, md, University of California, San Francisco, School of Medicine, San Francisco, California

The Cochrane Abstract is a summary of a review from the Cochrane Library. It is accompanied by an interpretation that will help clinicians put evidence into practice. Dr. Potter presents a clinical scenario and question based on the Cochrane Abstract, followed by an evidence-based answer and a critique of the review. The practice recommendations in this activity are available at http://www.cochrane.org/reviews/ en/ab001877.html.

Clinical Scenario

A healthy 44-year-old woman with no family history of breast cancer has never had a mammogram. Her best friend was recently diagnosed with breast cancer.

Clinical Question

How should physicians counsel women about mammography?

Evidence-Based Answer

Studies of mammography show a 0.1 percent absolute reduction in breast cancer mortality with mammography. This means that if 2,000 women are offered mammography over 10 years, one woman would have her life prolonged, 10 healthy women would be treated unnecessarily for breast cancer, and about 200 women would undergo psychological distress and additional testing because of false-positive results. Women should be informed of the potential benefits and harms of mammography before undergoing the screening test at any age.1

Practice Pointers

This Cochrane review updates a controversial 2001 review that concluded that mammography at any age is unjustified. This updated review concludes that the large randomized trials of mammography conducted in the past 40 years indicate that mammography can reduce breast cancer mortality by 15 to 20 percent. However, the authors remain skeptical about the balance of benefits and harms from mammography at any age. False-positive mammography results are much more common than true positives, and there is a potential for the overdiagnosis of nonaggressive or more-advanced, but indolent, forms of ductal carcinoma in situ (DCIS).

Most authorities who have weighed the same evidence included in this Cochrane review have endorsed mammography screening every one or two years for women 40 years and older.2,3 They acknowledge that women 40 to 49 years of age have less to gain from screening than women 50 to 69 years of age, and that women 70 years and older are likely to benefit only if they are healthy.2,3 Studies of U.S. women have generally found a high tolerance of false-positive results, but the extent and consequences of overdiagnosis continue to be a source of debate.4,5 One recent and carefully designed study found an overdiagnosis rate of only 10 percent, which is significant but substantially less than that estimated in this Cochrane review.6

Given the uncertainties, clinicians should be prepared to counsel average-risk patients who are considering mammography about the facts related to breast cancer and screening. Breast cancer is the second leading cause of cancer death in the United States, with approximately 40,000 deaths predicted in 2007.7 As the incidence of early-stage DCIS has increased, the incidence of invasive breast cancer has decreased. Overall, the rate of breast cancer mortality in the United States decreased by 2.3 percent annually between 1990 and 2002. This decline in the mortality rate may be caused in part by more screening, better treatment, and other factors.8

The Centers for Disease Control and Prevention estimates that a woman's chance of dying from breast cancer when she is 40 to 49 years of age is 0.2 percent (one in 500); this increases to 0.4 percent (one in 250) for a woman 50 to 59 years of age and to 0.7 percent (one in 140) for a woman 60 to 69 years of age.9 In 2002, the U.S. Preventive Services Task Force estimated that 1,792 women 40 to 49 years of age must be screened for 14 years to prevent one death, and 838 women 50 to 69 years of age must be screened for 14 years to prevent one death.2 After considering this information, women who are at average risk of breast cancer may reasonably come to different personal conclusions about having a mammogram.

The National Cancer Institute has developed an online risk-assessment tool (http://www.cancer.gov/bcrisktool) that includes factors other than current age such as age at menarche, age at first childbirth, ethnicity, and family history. Such tools may help a patient make decisions about mammography in the context of her individual risk. Some factors that have been proven to increase the risk of breast cancer, such as extensive mammographic breast density,10 are not yet included in the tool. For women with a high risk of breast cancer, more intensive interventions such as genetic counseling and breast magnetic resonance imaging may be indicated.11

Unfortunately, even with all the available facts about breast cancer screening, decisions about obtaining mammography can be complicated. A recent study found that women with abnormal mammography results and subsequent DCIS diagnoses would have preferred more information about the implications of mammography before they were originally screened.12 Ultimately, before deciding whether to be screened, women should receive a careful assessment of their personal risk of breast cancer and counseling about their individualized benefits versus harms from mammography.

Address correspondence to Michael B. Potter, MD, potterm@fcm.ucsf.edu. Reprints are not available from the author.

Author disclosure: Nothing to disclose.

REFERENCES

1. Gøtzsche PC, Nielsen M. Screening for breast cancer with mammography. Cochrane Database Syst Rev 2006;(4):CD001877.

2. Humphrey LL, Helfand M, Chan BK, Woolf SH. Breast cancer screening: a summary of the evidence for the U.S. Preventive Services Task Force. Ann Intern Med 2002;137(5 pt 1):347-60.

3. Elmore JG, Armstrong K, Lehman CD, Fletcher SW. Screening for breast cancer. JAMA 2005;293:1245-56.

4. Schwartz LM, Woloshin S, Sox HC, Fischhoff B, Welch HG. US women's attitudes to false positive mammography results and detection of ductal carcinoma in situ: cross sectional survey. BMJ 2000;320:1635-40.

5. de Roos MA, van der Vegt B, de Vries J, Wesseling J, de Bock GH. Pathological and biological differences between screen-detected and interval ductal carcinoma in situ of the breast. Ann Surg Oncol 2007;14:2097-2104.

6. Zackrisson S, Andersson I, Janzon L, Manjer J, Garne JP. Rate of over-diagnosis of breast cancer 15 years after end of Malmo mammographic screening trial: follow-up study. BMJ 2006;332:689-92.

7. American Cancer Society. Cancer facts and figures 2007. Accessed July 5, 2007, at: http://www.cancer.org/downloads/STT/CAFF2007PWSecured.pdf.

8. Berry DA, Cronin KA, Plevritis SK, Fryback DG, Clarke L, Zelen M, et al., for the Cancer Intervention and Surveillance Modeling Network (CISNET) Collaborators. Effect of screening and adjuvant therapy on mortality from breast cancer. N Engl J Med 2005;353:1784-92.

9. Centers for Disease Control and Prevention. Risk of breast cancer by age. Accessed June 16, 2007, at: http://www.cdc.gov/cancer/breast/statistics/age.htm.

10. Boyd NF, Guo H, Martin LJ, Sun L, Stone J, Fishell E, et al. Mammographic density and the risk and detection of breast cancer. N Engl J Med 2007;356:227-36.

11. Saslow D, Boetes C, Burke W, Harms S, Leach MO, Lehman CD, et al., for the American Cancer Society Breast Cancer Advisory Group. American Cancer Society guidelines for breast screening with MRI as an adjunct to mammography. CA Cancer J Clin 2007;57:75-89.

12. Prinjha S, Evans J, McPherson A. Women's information needs about ductal carcinoma in situ before mammographic screening and after diagnosis: a qualitative study. J Med Screen 2006;13:110-4.

Cochrane Briefs

Advance Provision for Emergency Oral Contraception

Clinical Question

Does providing women with emergency oral contraception in advance for use as needed change pregnancy rates, frequency and timing of contraceptive use, risk of sexually transmitted infections, or sexual behavior?

Evidence-Based Answer

Providing oral emergency contraceptives in advance to fertile women for use after unprotected sexual intercourse (i.e., advance provision) does not affect pregnancy rates, condom use, sexually transmitted infection rates, or type of contraception used. Advance provision more than doubles the odds that a woman will use emergency contraception once and more than quadruples the odds that she will use it two or more times. It also reduces the time from sexual intercourse to emergency contraceptive use by about 15 hours.

Practice Pointers

To increase the availability and use of emergency contraception, the American College of Obstetricians and Gynecologists recommends one 1.5-mg dose of levonorgestrel (Plan B) or two 0.75-mg doses taken 12 to 24 hours apart for women who have had unprotected or inadequately protected sexual intercourse.1 This practice guideline supports advance provision. The American Academy of Pediatrics has a similar policy.2 The American Academy of Family Physicians does not specifically address advance provision.3 Although combined contraceptive pills and mifepristone (Mifeprex) can be used for emergency contraception, levonorgestrel is better tolerated, is more effective, and is approved by the U.S. Food and Drug Administration for over-the-counter distribution.

This Cochrane review included randomized controlled trials comparing advance provision with standard access to emergency contraception. The review included eight trials (6,389 total participants); five of the trials were conducted in the United States. Two studies had the power to show a difference in pregnancy rates. Control groups received general contraceptive counseling, information about emergency contraceptives, and/or access to emergency contraception on request. Most of the trials provided one to three courses of levonorgestrel and followed patients for three to 12 months.

No study found a difference in pregnancy rates. Women who had advanced access to emergency contraception were about 2.5 times more likely to use it once and over four times more likely to use it two or more times. These women were also more likely to take the contraception an average of about 15 hours sooner after sexual intercourse than those in the control groups. The three studies that measured rates of sexually transmitted infections did not find a difference between groups. The five studies that reported on contraception use did not find differences between groups in the type or frequency of contraception use, including condom use. The six studies that compared frequency of unprotected sexual intercourse did not find a difference between groups. No adverse events were reported in any of the studies.

Although most women took the first contraceptive pill as directed, in one study, 17 percent of women who received advanced access took the second pill incorrectly. Therefore, single-dose regimens may be preferable. Providing women with advanced access to emergency contraception appears to be safe but does not reduce pregnancy rates on a population level. However, individual women might benefit because advance provision increases the speed and frequency of contraceptive use.

CLARISSA KRIPKE, MD

Source: Polis CB, Schaffer K, Blanchard K, Glasier A, Harper CC, Grimes DA. Advance provision of emergency contraception for pregnancy prevention (full review). Cochrane Database Syst Rev 2007;(2):CD005497.

REFERENCES

1. American College of Obstetricians and Gynecologists. Emergency contraception. ACOG Practice Bulletin No. 69, December 2005. Clinical management guidelines for obstetrician-gynecologists. Obstet Gynecol 2005;106:1143-52.

2. American Academy of Pediatrics Committee on Adolescence. Emergency contraception. Pediatrics 2005;116:1026-35.

3. American Academy of Family Physicians. Over-the-counter emergency contraception. Substitute resolution No. 515. Accessed July 16,
2007, at: http://www.aafp.org/online/en/home/aboutus/theaafp/congress/resolutions.mem.html (click Resolution Summary; password required).

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