NEJM: Screening mammography recommended for most women
 |
Warner reviewed key data about breast cancer and mortality, emphasizing:
- Breast cancer is the leading cause of death from cancer in women.
- Tumor stage is the key determinant of outcome for breast cancer.
- The ideal screening modality detects a tumor before it is palpable.
- Breast cancer mortality has fallen 2.2 percent annually in the U.S. since 1990, which is equally attributable to screening mammography and advances in adjuvant therapy.
“The decision to screen either a particular population or a specific patient for a disease involves weighing benefits against costs. … The ratio of benefit to cost varies significantly with the patient’s age,” wrote Warner, adding that screening is universally recommended for women ages 50 to 69.
A meta-analysis of screening mammography in this age group indicates a 14 percent reduction in breast cancer mortality for women in their 50s and 32 percent for those in their 60s.
For women ages 70 and older, however, data are limited. Independent statistical models demonstrate two additional deaths would be prevented per 1,000 women screened from ages 70 to 74 years, with little benefit beyond age 74. In addition, women with serious coexisting illnesses or a life expectancy of less than five to 10 years should not be screened.
The genuine conundrum for physicians regards recommendations for women ages 40 to 49. Warner observed that no single randomized trial has clearly linked mammographic screening with a reduction in mortality in this age group. However, “several meta-analyses that included this age group have shown breast cancer mortality is significantly reduced (by 15 to 20 percent).”
According to Warner, the USPSTF primarily based its decision to revise screening mammography recommendations on the Age trial, which found screening mammography had a nonsignificant reduction in risk among women in their 40s. But Warner outlined flaws in the trial, including its use of single-view screening, failure to achieve sample size and 70 percent compliance rate.
In addition, she noted that screening women under the age of 50 gains greater number of years of life expectancy by preventing breast cancer death in younger women.
Warner addressed other issues related to the USPSTF recommendations, referring to statistical models that show biennial screening maintains 81 percent of the benefit of annual screening among women ages 50 to 69, while annual screening prevented two additional deaths per 1,000 women screened. Two-year screening intervals are not associated with an increased risk of late-stage disease among women 50 and older, Warner added.
She noted that digital mammography improves the sensitivity of film-screen mammography from 51 percent to 78 percent for women under the age of 50, and offers comparable advantages for premenopausal women and those with dense breasts.
Warner pointed out that the incidence of ductal carcinoma in situ (DCIS) has climbed since the introduction of screening mammography and now accounts for 25 percent of all breast cancer cases, with most DCIS detected by imaging. DCIS tumors may not grow or become invasive, yet patients are typically treated with lumpectomy and radiation therapy.
The author also reviewed areas of uncertainty. Specifically, although individual risk stratification is desirable, the National Cancer Institute’s Breast Cancer Risk Assessment Tool is not accurate in predicting individual risk, and the Tyrer-Cuzick model, which includes additional variables, has not yet been validated.
Previous randomized trials focused largely on white women. And the generalizability of findings to African-American and Asian women is unclear. Young African-American women have a higher incidence of breast cancer and a higher proportion of high-grade cancers negative for estrogen and progesterone receptors, which may make their tumors less amenable to detection by screening, offered Warner. In contrast, Asian women have a relatively lower incidence of breast cancer and greater breast density, which may boost screening benefits.
Finally, Warner turned to other screening methods. Ultrasound delivers an up to 30 percent increase in detection of breast cancer in women with dense breasts, but it is associated with false positive results ranging from 2.4 to 12.9 percent. MRI doubles the sensitivity among high-risk women, but because of its higher rate of false positives and cost, is not recommended for general screening. Breast tomosynthesis has not yet demonstrated improved diagnostic sensitivity compared with mammography.
Warner concluded, “I would recommend digital mammography for screening women in their 40s, older premenopausal women and women of any age whose breasts are heterogeneously dense or very dense.” She also reinforced the value of annual or biennial mammography screening for women 50 to 69 years of age with a life expectancy of five years or more and recommended that screening decisions for women older than 70 be based on life expectancy and individual preferences.
For more about screening mammography, please read Health Imaging & IT’s September cover story “USPSTF Guidelines Two Years Later: The Fallout Continues.”