Breast cancer is the second most common malignancy of women. The American Cancer Society estimates that in the U.S. in 2009, 67,280 women will have been diagnosed with new cases of in situ cancer, 192,370 women will have been newly diagnosed as having invasive breast cancer, and there will be 40,170 deaths due to this disease. In the general population, the cumulative risk of being diagnosed with breast cancer by age 70 is estimated to be 6% (lifetime risk of 13%). Ductal carcinoma, including ductal carcinoma in situ (DCIS), is the most common malignancy of the breast. It arises within the ducts of the breast. DCIS is early breast cancer confined to the inside of the ductal system, and invasive (also called infiltrating) ductal carcinoma is a later stage that has broken through the walls of the ducts and invaded nearby tissues. Lobular carcinoma is similar to ductal carcinoma, first arising in the terminal ducts of the lobules and then invading through the walls of the ducts and into nearby tissues. Atypical lobular hyperplasia (ALH) and lobular carcinoma in situ (LCIS) are caused by abnormal cellular proliferation within the terminal ducts of the lobules. The two conditions are distinguished primarily by the degree to which the ducts are filled by cells. Women diagnosed with ALH or LCIS are at elevated risk of developing an invasive carcinoma in the future. Other types of benign breast abnormalities that have been linked to an elevated risk of invasive carcinoma or a finding of associated invasive carcinoma upon excision are atypical ductal hyperplasia (ADH), papillary lesions, and radial scars. Breast cancer is usually first detected by feeling a lump on physical examination or by observing an abnormality during x-ray screening mammography. Survival rates depend on the stage of disease at diagnosis. At stage 0 (carcinoma in situ) the five-year survival rate is close to 100%. The five-year survival rate for women with stage IV (cancer that has spread beyond the breast) is only 27%. These observations suggest that breast cancer mortality rates can be significantly reduced by identifying cancers at earlier stages. Because early breast cancer is asymptomatic, the only way to detect it is through population-wide screening. Mammography is a widely accepted method for breast cancer screening. Mammography uses x-rays to examine the breast for clusters of microcalcifications, circumscribed and dense masses, masses with indistinct margins, architectural distortion compared with the contralateral breast, or other abnormal structures. The American College of Radiology has created a standardized system for reporting the results of mammography, the Breast Imaging Reporting and Data System (BI-RADS(r) ). There are seven categories of assessment and recommendation: 0 Need additional imaging evaluation and/or prior mammograms for comparison 1 Negative 2 Benign finding 3 Probably benign finding. Initial short interval follow-up suggested 4 Suspicious abnormality. Biopsy should be considered. 5 Highly suggestive of malignancy. Appropriate action should be taken. 6 Known biopsy-proven malignancy. Appropriate action should be taken. This systematic review was commissioned by the Agency for Healthcare Research and Quality (AHRQ) to address the following Key Questions; they include, but are not limited to: 1. In women with a palpable or non-palpable breast abnormality, what is the accuracy of different types of core-needle breast biopsy compared with open biopsy for diagnosis? 2. In women with a palpable or non-palpable breast abnormality, what are the harms associated with core-needle breast biopsy compared to the open biopsy technique in the diagnosis of breast cancer? 3. How do open biopsy and various core-needle techniques differ in terms of patient preference, availability, costs, availability of qualified pathologist interpretations, and other factors that may influence choice of particular technique?