1998a, b). Although certain mammographic images (e.g. a spiculated mass) are characteristic of cancer, no criteria allow the radiologist to absolutely differentiate benign from malignant lesions (Osuch, 1996; Talamonti and Morrow, 1996). Given this significant overlap in the appearance of benign and malignant lesions on mammography, other tests are necessary to rule out a malignancy. Ultrasound may be useful to differentiate cysts from solid masses; however, a biopsy to obtain a pathologic diagnosis is often the only way to determine whether a lesion is benign or malignant. Any persistent breast mass that is not determined to be a simple cyst either by aspiration of clear fluid or by ultrasound characteristics should have a pathologic diagnosis, either through fine needle aspiration or excisional biopsy. Biopsy is the gold standard. Fine needle aspiration can falsely identify from less than 1 percent to 35 percent of cancers as negative, but accuracy improves when it is used in conjunction with clinical exam and simultaneous mammography in a procedure referred to as triple diagnosis (Kaufman et al., 1994).

Studies of screening mammography suggest significant variation in both the technical quality of radiographic images and their interpretation. A series of evaluations by the Food and Drug Administration (FDA) in 1985, 1988, and 1992 suggested widespread variation in mammographic image quality (Houn and Finder, 1997). Although improvement was noted overall, with 86 percent of images being acceptable in 1992 compared to only 64 percent in 1985, a significant problem in image quality remained, which was felt to be attributable to differences in technique (Segal, 1994). At the urging of the FDA, the American College of Radiology developed a voluntary accrediting process for mammography facilities in 1987 to attempt to correct this problem (Houn and Finder, 1997).

Concern about the quality of mammography led Congress to pass the Mammography Quality Standards Act in 1992, which established minimum national quality standards for mammography facilities (USGAO, 1998a, b). During the first three years of FDA inspections, compliance with national standards and x-ray quality improved. Before the act took effect, 11 percent of facilities tested were unable to pass image quality tests; in 1996, the nationwide figure was 2 percent (USGAO, 1998a, b).

The FDA has established federal qualification requirements for physicians who interpret mammograms, but each facility uses its own data to monitor physicians' performance on interpretation (USGAO, 1998a, b). Wide variation in diagnostic accuracy has been observed. According to a recent study, radiologists' ability to identify breast cancer from a screening mammogram (with biopsy as the gold standard) ranged from 47 to 100 percent, with a mean of 79 percent, and their ability to correctly rule out breast cancer varied from 36 to 99 percent. This study involved 108 radiologists practicing in 50 participating facilities randomly sampled from 4,611 ACR-accredited mammography centers (Beam et al., 1996).

The quality of the breast biopsy procedure is important so that the clinicians who make treatment recommendations to women with a breast lesion or with breast cancer have accurate information. Multiple steps in the process of breast biopsy are critical to ensuring that results are accurate, including the biopsy procedure itself (which may be a fine needle aspiration, a stereo-tactic core biopsy, an open biopsy, or a needle localization procedure followed by a biopsy), the tissue preparation, the cytopathology interpretation, the assessment of estrogen receptor and progesterone receptor status, and the pathology report that communicates all of the findings. A few studies have addressed the quality of some of these steps. A single community-based study in New Hampshire assessed the degree of diagnostic agreement among general pathologists reading an investigator-defined set of breast tissue specimens obtained via core and excisional biopsies

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