Mammography

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Chapter 157 Mammography

THE CHALLENGE

To improve the use of breast imaging to detect occult disease.

Scope of the Problem: Widespread use of mammography has been credited with reducing the mortality rate from breast cancer by up to 30%. Unfortunately, not all women receive appropriate screening on a regular basis. One study indicated that only 39% of women aged 50 to 59 and 36% of women aged 60 to 69 had had a mammogram in the preceding year. In another study, only 24% of women older than age 65 followed the current recommendations for annual examinations. It has been estimated that breast cancer mortality could be reduced by as much as one half if all women older than 40 received annual screening. In one study, 6 cancers per 1000 screening mammograms were found, and 3 additional cancers per 1000 annual repeat studies were detected.

Objectives: To appropriately use mammography for the evaluation of breast complaints and to improve compliance with screening guidelines.

TACTICS

Relevant Pathophysiology: Mammography is the best mode of screening for early lesions currently available. Mammography localizes, documents, objectifies, and identifies other occult pathologic changes. Approximately 85% of breast cancers found by mammography are early-stage lesions versus 54% to 70% found by physicians and 38% to 64% of tumors found by the patient herself during breast self-examination. Approximately 35% of breast cancers are found with an abnormal mammogram, without a palpable mass present. Mammography can identify small lesions (1 to 2 mm), calcifications, or other changes suspicious for malignancy about 2 years before a lesion is clinically palpable. Ten-year disease-free survival for patients with these lesions is 90% to 95%. The average lesion found on breast self-examination is 2.5 cm, and half of these patients have nodal involvement. For these patients, 10-year survival falls to between 50% and 70%. More than one third of occult breast cancers have calcifications, making the otherwise-undetected tumors visible through mammography.

Strategies: The American Cancer Society guidelines for mammographic screening are the following:

• Mammography every 1 to 2 years from age 40 to 49.

• Annual mammogram from age 50 on. (If the patient has a first-degree relative with premenopausal breast cancer, screening should begin about 5 years before the age at which the relative’s cancer was diagnosed.)

• For patients at increased risk for breast cancer (strong family history or genetic abnormality such as mutations of BRCA1 or BRCA2) mammography should be augmented by magnetic resonance imaging (MRI) studies.

Patient Education: Instruction on need for and timing of mammography; American College of Obstetricians and Gynecologists Patient Education Pamphlet AP026 (Detecting and Treating Breast Problems), AP076 (Mammography), AP145 (Breast Self-Examination).

IMPLEMENTATION

Special Considerations: Mammography in younger women is more difficult to interpret than in older women because of the greater tissue density present during the reproductive years. Whereas the increasing ability to diagnose cancer in older women parallels their increasing risk, breast cancers in younger women are more easily missed. This diagnostic difficulty and the relatively higher rate of false-positive study results that necessitate further evaluation have raised questions about routine screening of women younger than age 50. The finding of clusters of calcification that often are associated with cancer is nonspecific. Of calcification clusters found on mammography, 75% result from benign disease. Overall, mammography is approximately 85% accurate in diagnosing malignancy, with a 10% to 15% false-negative rate. For this reason, it provides an adjunct to clinical impressions and the definitive procedure of biopsy, but it does not replace them. Approximately 10% of mammographic studies require additional views. Between 1% and 2% of screening studies necessitate histologic evaluation to establish a diagnosis. Mammographic radiation exposure is minimal (less than 1 rad). Based on this level of exposure, mammography might induce up to 5 new lifetime cancers for every 1 million women of age 40 to 44 screened and less than 1 per 1 million for women aged 60 to 64 (background risk is 115 and 292 for these age groups, respectively). Therefore, the risk of death caused by radiation exposure is roughly equivalent to the risk of death encountered by driving a car 220 miles, riding a bicycle for 10 miles, or smoking 1.5 cigarettes.

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