The mammography controversy: When should you screen?

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Applied Evidence

The mammography controversy: When should you screen?

J Fam Pract. 2011 September;60(9):524-531

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References

1. Jemal A, Siegel R, Ward E, et al. Cancer statistics, 2009. CA-Cancer J Clin. 2009;59:225-249.

2. National Cancer Institute. Fact sheet. Probability of breast cancer in American women. Available at: http://www.cancer.gov/cancertopics/factsheet/detection/probability-breast-cancer. Accessed August 23, 2011.

3. Berry DA, Cronin KA, Plevritis SK, et al. Effect of screening and adjuvant therapy on mortality from breast cancer. N Engl J Med. 2005;353:1784-1792.

4. Humphrey LL, Helfand M, Chan BK, et al. Breast cancer screening: a summary of the evidence for the US Preventive Services Task Force. Ann Intern Med. 2002;137(5 part 1):347-360.

5. American College of Obstetricians and Gynecologists. Annual mammograms now recommended for women beginning at age 40. July 20, 2011. Available at: http://www.acog.org/from_home/publications/press_releases/nr07-20-11-2.cfm. Accessed August 15, 2011.

6. US Preventive Services Task Force. Screening for breast cancer. July 2010. Available at: http://www.uspreventiveservicestaskforce.org/uspstf/uspsbrca.htm. Accessed August 15, 2011.

7. Nelson HD, Tyne K, Naik A, et al. Screening for breast cancer:. an update for the US Preventive Services Task Force. Ann Intern Med. 2009;151:727–737, W237–742.

8. US Preventive Services Task Force. Screening for breast cancer. US Preventive Services Task Force recommendation statement. Ann Intern Med. 2009;151:716-726.

9. Smith RA, Cokkinides V, Brooks D, et al. Cancer screening in the United States, 2010: a review of current American Cancer Society guidelines and issues in cancer screening. CA-Cancer J Clin. 2010;60:99-119.

10. Lee CH, Dershaw DD, Kopans D, et al. Breast cancer screening with imaging: recommendations from the Society of Breast Imaging and the ACR on the use of mammography, breast MRI, breast ultrasound, and other technologies for the detection of clinically occult breast cancer. J Am Coll Radiol. 2010;7:18-27.

11. Mandelblatt JS, Cronin KA, Bailey S, et al. Effects of mammography screening under different screening schedules: model estimates of potential benefits and harms. Ann Intern Med. 2009;151:738-747.

12. American College of Obstetricians and Gynecologists. Practice bulletin no. 122: breast cancer screening. Obstet Gynecol. 2011;118:372-382.

13. Madigan MP, Ziegler RG, Benichou J, et al. Proportion of breast cancer cases in the United States explained by well-established risk factors. J Natl Cancer Inst. 1995;87:1681-1685.

14. Kalager M, Zelen M, Langmark F, et al. Effect of screening mammography on breast-cancer mortality in Norway. N Engl J Med. 2010;363:1203-1210.

15. Welch HG. Screening mammography—a long run for a short slide? N Engl J Med. 2010;363:1276-1278.

16. Hellquist BN, Duffy SW, Abdsaleh S, et al. Effectiveness of population-based service screening with mammography for women ages 40 to 49 years: evaluation of the Swedish Mammography Screening in Young Women (SCRY) cohort. Cancer. 2010;117:714-722.

17. Hendrick RE, Helvie MA. United States Preventive Services Task Force screening mammography recommendations: science ignored. AJR Am J Roentgenol. 2011;196:W112-W116.

18. Gotzche PC, Nielsen M. Screening for breast cancer with mammography. Cochrane Database Syst Rev. 2011;(1):CD001877.-

19. Autier P, Boniol M, Gavin A, et al. Breast cancer mortality in neighbouring European countries with different levels of screening but similar access to treatment: trend analysis of WHO mortality database. BMJ. 2011;343:d4411.-

20. When evidence collides with anecdote, politics, and emotion: breast cancer screening [editorial]. Ann Intern Med. 2010;152:531-532.

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22. Australian Screening Mammography Decision Aid Trial. Available at: http://www.mammogram.med.usyd.edu.au/. Accessed August 15, 2011.

23. Barratt A, Howard K, Irwig L, et al. Model of outcomes of screening mammography: information to support informed choices. BMJ. 2005;330:936.-

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The reduction in breast cancer deaths associated with annual screening is about the same for both groups, according to ACOG—16% for women in their 40s, and 15% for women 50 and older.¹² The 5-year survival rate for women whose breast tumors are discovered before they’re palpable and before the cancer has spread is 98%.¹³

ACOG also interpreted the potential harms associated with screening differently. The organization acknowledges that false-positive findings are a continuing concern, but has determined that the benefits of annual screening outweigh the risks.¹²

TABLE 2
Breast cancer and mammography: How age affects outcomes

Breast cancer
Age range (y)	Probability (%)^2,12
40-49	1 in 69 (1.4)
50-59	1 in 42 (2.4)
60-69	1 in 29 (3.5)
	*Sojourn time^5,12**
40-49	2-2.4 y
≥70	4-4.1 y
	NNS to prevent 1 breast cancer death⁸
40-49	1904
50-59	1339
60-69	377
NNS, number needed to screen. *Interval between the time a breast tumor is detectable by mammography and it becomes symptomatic.

Recent studies hit the headlines, but fail to lend clarity

Norwegian cohort study. One study examining the effect of mammography on breast cancer mortality in a large cohort of Norwegian women found that patients ages 50 to 69 who were screened biennially had a 10% reduction in breast cancer death.¹⁴ However, further analysis suggested that screening in and of itself accounted for only about one-third of the reduction—an absolute risk reduction of 2.4 deaths per 100,000 person-years. (The rest was attributed to other factors, such as advances in breast cancer awareness and treatment.¹⁴) The study was published in the New England Journal of Medicine along with an editorial suggesting that it might be time to consider the rather small effects of screening mammography.¹⁵

Swedish cohort study. A study involving a large cohort of Swedish women found that mammography screening was associated with a 29% reduction in breast cancer mortality for women between the ages of 40 and 49.¹⁶ Notably, however, the difference in relative risk (RR) for women who were invited to be screened (0.74; 95% confidence interval [CI], 0.66-0.83) vs those who underwent regular screening (0.71; 95% CI, 0.62-0.80) was small.

CISNET modeling study. In a study in the American Journal of Roentgenology, researchers used the same data and CISNET modeling as the USPSTF, but compared lives saved with biennial screening mammography starting at age 50 vs annual screening starting at 40. The researchers reported that for women ages 40 to 84 years, approximately 12 lives per 1000 women screened annually would be saved; for women between the ages of 50 to 74 years screened biennially, 7 lives per 1000 people screened would be saved. That translates into 71% more lives saved with annual, rather than biennial, screening—a reduction of approximately 23%.¹⁷

There was a downside, however: The researchers estimated that, on average, women who initiated annual mammography at age 40 would receive a false-positive result every 10 years, and be recalled for imaging every 12 years. Other potential (albeit rare) harms identified by the researchers: one false-positive biopsy (every 149 years), one missed case of breast cancer (every 1000 years), and one fatal radiation-induced breast cancer (every 76,000-79,000 years). ¹⁷

FAST TRACK

A 2011 Cochrane review found that mammography screening resulted in an estimated 15% decrease in breast cancer deaths—and a 30% increase in overdiagnosis and overtreatment.

2011 Cochrane review. In an update of a 2006 meta-analysis, Cochrane reviewers estimated that screening mammography results in a 15% decrease in breast cancer deaths (an absolute risk reduction of 0.05%).¹⁸ But screening also led to a 30% increase in overdiagnosis and overtreatment (an increase in absolute risk of 0.5%). That finding, which prompted the reviewers to conclude that it is not clear whether screening mammography does more good than harm, means that over the course of 10 years, for every 2000 women screened, 10 healthy women can expect to undergo unnecessary diagnostic procedures and receive unnecessary treatment.¹⁸

European trend analysis. A retrospective trend analysis published in the British Medical Journal in July 2011 is the latest assessment of the benefits of screening mammography.¹⁹ The researchers used WHO data to evaluate breast cancer mortality in several European countries, comparing nations with similar demographics and access to care but different levels of breast cancer screening. Their findings? From 1989 to 2006, reductions in breast cancer mortality were about the same in countries with similarities in levels of health care and demographics, regardless of mammography screening.¹⁹

How best to meet your patient’s needs

Where does this leave you? Supporters of the USPSTF’s recommendations have argued that they offer an evidence-based approach to mammography screening for women at average risk, and will help decrease excessive screening and the overdiagnosis, overtreatment, and psychological stress that often result. Critics maintain that trying to fit all women into a single model of breast cancer screening continues to be a problem—one that neither the USPSTF or ACOG has adequately addressed. The risks of breast cancer among various minority groups, for example, have not been taken into account.