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Current recommendations for screening mammography

Breast cancer is the most common cancer diagnosed in women and the second leading cause of cancer death in women in the United States. The American Cancer Society estimates that this year 180,200 new cases of invasive breast cancer will be diagnosed and 44,190 deaths will occur from breast cancer among U.S. women.

Between 1982 and 1987, breast cancer incidence rates increased about 4 percent each year. Most of this increase is attributed to a marked increase in the use of mammography, which provides better early detection of breast cancer. Recent data also show death rates have begun to decline. The largest factor for this decline is believed to be early detection.

Early detection
Early detection of breast cancer is achieved through screening mammography combined with a physical breast examination. The goal of screening mammography is to detect cancer at an early stage, when it is curable. Mammography detects 85 to 90 percent of clinically apparent breast cancer. An additional 10 to 15 percent of breast cancer, which goes undetected by mammography, is found through a physical breast exam. In women of average risk who receive mammography screenings, physicians expect to detect three breast cancers per 1,000 people. For every 1,000 women screened, 100 to 150 women will be recalled for additional mammographic views or a breast ultrasound. In this group, most women will have benign or probably benign changes that can be followed with mammography to confirm stability. Fifteen of these women will have changes suspicious enough to require a biopsy. And of those 15, three women will be diagnosed with cancer.

Screening data by age group
Randomized, controlled trials have shown a 25 to 30 percent reduction in mortality because of a screening mammo-graphy in women ages 50 and older. There is a consensus between health-care providers and national health agencies that a yearly screening mammography combined with a physical breast exam reduces mortality in women ages 50 to 70. In addition, women older than 70 clearly benefit from screening mammo-graphy, but other health factors need to be considered when recommending screenings to women in this age group. For this age group, biennial screenings may be as good as annual exams.Even more controversy exists concerning screening mammography for women ages 40 to 49. Breast cancer among women ages 40 to 49 is a major clinical problem. Breast cancer is the single leading cause of death among 40- to 49-year-old women in the United States. And cancer found in women younger than 50 years results in 20 percent of breast cancer deaths and nearly 40 percent of years of life expectancy lost. No single randomized trial using mammography as the sole screening modality has included a sufficient number of women ages 40 to 49 to show statistically significant mortality reduction. However, newer data and recent meta--analyses now show mortality reduction of up to 25 percent from screening women in this age group.

Mammograms are safe
There is no information to suggest that women are harmed by mammography, additional mammographic work-up or breast ultrasound. There is no measurable harm from the diagnostic radiation doses used for screening mammography. Mammography sensitivity is decreased in younger women with dense breast tissue. Fatty metamorphosis occurs gradually as women age. Breast density may increase in post-menopausal women placed on exogenous hormones. However, these factors should not negatively influence screening guidelines. Using current state-of-the-art mammographic techniques and liberal breast ultrasound in women with dense breast tissue, the screening sensitivity approaches that of women with fatty replaced breasts.

Ultrasound, a diagnostic tool
Breast ultrasound is a diagnostic tool that helps define abnormalities detected on clinical exam or mammography. High-resolution ultrasound with a 15 MHz probe allows us to accurately characterize lesions as benign or probably benign in cases such as fibrocystic disease and benign solid tumors, avoiding the need for intervention. About 70 percent of breast cancers will be evident with ultrasound. Currently this includes most lesions that distort the normal breast architecture or form solid suspicious masses. These lesions or masses have imaging characteristics much different than benign cysts or masses. Ultrasound also allows for percutaneous biopsy to be performed in a safe, cost effective and accurate fashion. New high- resolution breast ultrasound technology is focusing on detection of microcalcifications -- the earliest feature of many breast cancers. Previously, these were only detected by mammography. The ability to see calcifications with ultrasound makes it possible to percutaneously biopsy such lesions more easily than by the stereotactic mammographic biopsy technique. However, ultrasound is a diagnostic tool and should not be used as the sole screening method for breast cancer because it is less sensitive, more expensive and requires greater technical expertise than mammography.

Annual screenings begin at 40
The American Cancer Society, American College of Radiology and Society of Breast Imaging all recommend yearly screening mammographies to women 40 to 49 years old, with earlier screenings in women of high risk. There are 15 million women in the United States in this age group. One third of all breast cancers will develop in this age span. The number of breast cancers diagnosed in women ages 40 to 49 is only 8 percent fewer than in women ages 50 to 59, and the socioeconomic impact of a delayed diagnosis of breast cancer is greater in women ages 40 to 49. Below the age of 40, the incidence of breast cancer is very low, except for women with high-risk factors. This includes women with a prior diagnosis of breast cancer or cancer precursor, women with two or more first-degree relatives who developed pre-menopausal breast cancer and those who carry identified genetic alterations that increase the susceptibility to breast cancer. These women should consult with their physician about beginning yearly screenings before the age of 40.

Don't delay
Questioning the benefits of mammography for women ages 40 to 49 may cause significant harm from delayed diagnosis. Health-care professionals should actively encourage annual screening mammographies combined with physical breast examinations beginning at age 40.

References

1. Smart, C.R., Cancer 1995: 75:1619-1626.

2. Feig, S.A., Cancer 1995:75:2412-2419.

3. Tabar, L., Cancer 1995:75:2507-25.