A 52-year-old woman presents to your outpatient clinic with a newly palpable marble-sized lump in the upper outer quadrant of her right breast. The mass is firm and non-tender. She performs breast self-examinations regularly and first noticed the mass 3 weeks ago. Your examination confirms a palpable lesion. Annual screening mammograms at another facility have been negative, including the last one 6 months ago. The woman is otherwise in good health.
When she was younger, she had two pregnancies and gave birth to two children, whom she did not breastfeed. She reached menopause at age 49 and has never been on hormone replacement therapy. Neither she nor anyone in her family has had breast cancer, and she has never undergone breast biopsy.
She says that a woman she spoke with in the waiting room, a 2-year breast cancer survivor, told her that her primary cancer had been “finally diagnosed” with magnetic resonance imaging (MRI). This patient is now urging you to order an MRI. What should you do?
DIFFERENT IMAGING TESTS FOR DIFFERENT INDICATIONS
Different imaging tests are indicated in different situations. Screening mammography is the standard of care for women who have no signs or symptoms of breast cancer. When a screening examination shows abnormal or equivocal findings or when a patient presents with symptoms (eg, a palpable lesion, breast pain, nipple discharge), further characterization with a tailored imaging examination is warranted. Such an examination might include diagnostic mammography, ultrasonography, or MRI.
This article reviews MRI’s role in breast cancer management with respect to the other imaging tests currently in use.
MAMMOGRAPHY IS THE SCREENING TEST OF CHOICE
Screening mammography, as distinguished from diagnostic mammography, is an x-ray examination of breast tissue that obtains high-quality images while using a very low dose of ionizing radiation. It is performed with the breast tissue compressed to optimize image quality. The examination time is short, usually 15 to 20 minutes. No contrast agents are used. The malignant lesions it detects differ from normal fibroglandular tissue in their x-ray attenuation, appearing as asymmetric soft-tissue densities, architectural distortion, masses, or abnormal calcifications.
The American Cancer Society1 recommends mammography as the method of choice to screen for nonpalpable, clinically occult breast cancers in women over age 40 and in younger women with certain risk factors.
The rationale for screening mammography is supported by evidence of significant reductions in death rates from breast cancer in patients who undergo routine mammographic screening. Tabar et al,2 in the Swedish Two-County Trial, found a 30% lower rate of death from breast cancer in women ages 40 to 74 who were invited to undergo screening: the reduction was 34% for women age 50 to 74 and 12% for women age 40 to 49. The authors attributed the smaller benefit in the younger group to a tendency toward more rapid tumor progression in that age group.
Mammography is somewhat less sensitive and specific in women with dense breasts,3 in younger women, and in women on hormone replacement therapy.4 For example, a recent population-based study of seven mammography registries in the United States5 reported that the sensitivity of mammography for detecting breast cancer, adjusted for breast density and age, ranged from 63% for extremely dense breast tissue to 87% for entirely fatty breast tissue, and from 69% for women age 40 to 44 to 83% for women age 80 to 89. The adjusted specificities ranged from 89% for extremely dense breast tissue to 97% for entirely fatty breast tissue. The adjusted specificities in women not on hormone replacement therapy ranged from 91% for those age 40 to 44 to 94% for those age 80 to 89. In women on hormone replacement therapy, the adjusted specificity was about 92% for all ages taken together.
Digital is often better than film
Screening mammography has improved with the development of digital technology,6 in which images are acquired directly from an x-ray-sensitive solid-state receptor, without film. This process differs from digital computer-aided detection techniques, in which conventional analog films are optically scanned, generating a secondary digital image, which is then used for subsequent computerized analysis.
In 2005, the first large national trial comparing digital mammography with conventional mammography—the Digital Mammographic Imaging Screening Trial6—showed that digital mammography held a statistically significant advantage over conventional film-screen mammography in three subgroups7:
- Women under age 50
- Women with radiographically dense breast tissue
- Premenopausal or perimenopausal women. It is hoped that these encouraging results will be confirmed and extended by other trials now in progress.