Breast cancer is the most common type of cancer in women worldwide. About ten percent of women are confronted with breast cancer in their lives. In the year 2005, it was estimated that there would be approximately 212, 118 new cases of invasive breast cancer and about 41,250 deaths in the United States. Breast cancer is most effectively treated when detected at an early stage, and the survival probability of the patient is dependent on the tumor size at detection time. The larger the tumor size, the larger the probability for the presence of metastases in vital organs. Early detection of the tumor is critical for a good prognosis.
A number of different imaging methods for diagnosis and biopsy of suspicious lesions are available. X-ray mammography is the main tool used for the detection and diagnosis of breast malignancies, and it is currently the only medical imaging modality used in screening. Figure 13.1 shows two of the most common projections of mammogram: Figs. 13.1(a) and (b) are examples of mediolateral oblique (MLO) image, whereas Figs. 13.1(c) and (d) are examples of craniocaudal (CC) image. With about 70% sensitivity and 30% positive predictive value, mammography screening has been shown in clinical trials to reduce breast cancer mortality by 25% to 30% for women in the 50 to 70 age group. However, x-ray mammography has limited specificity and sensitivity. About 10% of all cancers are overlooked using x-ray mammography, especially those in dense breasts. It is estimated that approximately two-thirds of these missed cancers are detected retrospectively by radiologists. In addition, about two-thirds of lesions sent to biopsy turn out to be benign. This has led to the investigation of alternative imaging modalities such as ultrasound, magnetic resonance imaging (MRI), computed tomography (CT), positron emission tomography (PET), etc. for the detection and diagnosis of breast cancer.
Ultrasound has become a valuable tool to use with mammograms because it is widely available and less expensive than other options. Breast ultrasound is used to target a specific area of concern found by the mammogram. It is a widely accepted adjunct to mammography in patients with palpable masses or symptomatic breast disease. It is well established that breast ultrasound can distinguish solid from cystic masses with an accuracy approaching 100%, and can detect lesions that are not mammographically visible.
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