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Stereotactic or ultrasound-guided needle core breast biopsies (NCBB) are now routinely performed to assess suspicious microcalcifications or non-palpable masses detected by screening mammography. This approach has been shown to have high sensitivity and specificity in establishing the diagnosis of fibrocystic lesions, ductal carcinoma in situ (DCIS), and invasive carcinoma (1). As more NCBB are being performed, pathologists are encountering lesions with features of atypical ductal hyperplasia (ADH) or atypical lobular hyperplasia (ALH). There are two issues that impact the clinical evaluation of patients with atypical lesions in NCBB samples. First, malignant lesions are known to frequently coexist with ADH/ALH, either within the same segment of breast tissue or in different quadrants (the latter as a manifestation of so-called field effect alteration). Because of partial/limited sampling, it is thus theoretically possible that at least some patients with atypia on NCBB may harbor occult DCIS. This problem is highlighted by the consideration that histologic distinction between ADH and DCIS is partially quantitative in nature (2, 3). Second, microfocal lesions may be missed during the process of trimming the block (so-called sectioning artifact). This problem is exacerbated if cores are fragmented or associated with crushing,

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