Mammography at age 40? A risk-based strategy

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Applied Evidence

Mammography at age 40? A risk-based strategy

J Fam Pract. 2013 November;62(11):630-631, 636-638

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References

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2. Brawley OW. Risk-based mammography screening: an effort to maximize the benefits and minimize the harms. Ann Intern Med. 2012;156:662-663.

3. Hendrick RE, Smith RA, Rutledge JH 3rd, et al. Benefit of screening mammography in women aged 40-49: a new meta-analysis of randomized controlled trials. J Natl Cancer Inst Monogr. 1997;22:87-92.

4. Kerlikowske K, Grady D, Ernster V. Benefit of mammography screening in women ages 40-49 years: current evidence from randomized controlled trials. Cancer. 1995;76:1679-1681.

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6. Warner E. Breast-cancer screening. N Engl J Med. 2011;365:1025-1032.

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8. 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.

9. Qaseem A, Snow V, Sherif K, et al; Clinical Efficacy Assessment Subcommittee of the American College of Physicians. Screening mammography for women 40 to 49 years of age: a clinical practice guideline from the American College of Physicians. Ann Intern Med. 2007; 146:511-515.

10. American Academy of Family Physicians. AAFP screening recommendation. Breast cancer, mammography before age 50. Available at: http://www.aafp.org/online/en/home/clinical/exam/ae.html. Accessed September 25, 2012.

11. Institute for Clinical Systems Improvement (ICSI) Breast cancer screening recommendations. Available at http://www.icsi.org/breast_disease_diagnosis/diagnosis_of_breast_disease_2.html. Accessed September 25, 2012.

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The impact of a false positive lingers. A cohort study that followed 454 women for 3 years after they received a false positive mammogram result found that it continued to have a negative psychological impact on them.²⁰

A risk-based screening approach

With no clear consensus on when to begin screening, primary care physicians and their patients would be wise to adopt a risk-based approach. Risk-based screening would focus efforts on women ages 40 to 49 who are more likely to benefit from screening mammography, which would represent a more effective use of resources.² To implement such an approach, it is critical to know the magnitude of risk reduction that would tip the balance of benefits and harms in favor of early screening, and which risk factors are associated with such an elevated risk (TABLE 2).²¹

A recent comparative modeling study found that for women with a 2-fold increased risk for breast cancer, the benefits and risks of starting biennial screening at age 40 are about the same as that of women at average risk who start biennial screening at age 50. As biennial screening at age 50 is widely recommended, the results of this study suggest that ≥2-fold risk is a useful threshold in determining when to start mammography screening for women in their 40s.²¹

The traditional counseling of women about breast cancer risks focuses on parity and age of first delivery, breastfeeding, obesity, and alcohol use, in addition to family history. However, none of these has an RR >1.5.²²

Two risk factors are associated with ≥2-fold RR for breast cancer:
• having one or more first-degree relatives with breast cancer
• having extremely dense breasts.
A prior breast biopsy is also associated with a high RR (1.87).²¹

Does your patient have dense breasts? A baseline mammogram is necessary to determine a woman’s breast density. The American College of Radiology developed BI-RADS (Breast Imaging Reporting and Data System) to standardize the reporting of density on mammograms.²³ BI-RADS has 4 categories of breast density:

1. Breast tissue is almost entirely fatty. (Adipose tissue is radiolucent and makes the mammogram easier to read.)
2. There are scattered fibroglandular densities in the breast.
3. The breasts are heterogeneously dense.
4. The breasts are extremely dense.

When there is a discrepancy between the density of the left and right breasts, radiologists are instructed to use the higher density.²³ Another method of documenting density assesses the percentage of the breast tissue that is dense as compared to fatty tissue.

Increased density (BI-RADS category 3 or 4) likely accounts for a sizeable proportion of nonfamilial breast cancers.²⁴ In a large case control study (N=1112), density in ≥75% of the breast was associated with 26% of all breast cancers diagnosed in women under 56 years.²⁵ While a number of other risk factors for breast cancer are related to breast density (nulliparity, positive family history of breast cancer, and hormone therapy), higher density is associated with large increased risks of breast cancer independent of the other factors.²⁴

Initiate regular screening for women at high risk

Most high-risk women should have regular screening beginning at age 40. The American Cancer Society recommends screening with magnetic resonance imaging (MRI) as opposed to mammography for women with ≥20% lifetime risk of developing breast cancer.²⁶

Adding an annual ultrasound to mammography may be another method of screening for high-risk women. A study of 2809 women with elevated breast cancer risk and dense breasts demonstrated that the addition of annual screening with either ultrasound or MRI detected an additional 3.7 cancers per 1000 women per year beyond mammography alone.²⁷ In that study, however, there was a significant number of false positive results, as well.

MRI is not indicated for women with a 15% to 20% lifetime risk. These women will benefit from routine screening starting at age 40, as well as genetic counseling if they have a family history of breast cancer. Increased breast density can also make mammograms harder to read, and there is concern that density can mask an early cancer. In fact, multiple studies have refuted that claim.²⁸ Breast density does tend to decrease with age, but the relationship between increased density and elevated risk of breast cancer persists through all age groups.

Get a baseline mammogram for those at lower risk

One approach to risk-based screening is to recommend that all women at average risk have an initial screening mammogram at age 40 to determine breast density and discuss other pertinent risk factors. If they are found to have BI-RADS density category 3 or 4, regular screening mammography throughout their 40s is a reasonable approach.