Inconclusive or erroneous fine-needle aspirates of breast with adequate and representative material: a cytologic/histologic study.

Adequately cellular and representative fine-needle aspirates (FNAs) of breast have a high diagnostic accuracy. There is, however, a recognized category designated as "gray zone" where a definitive diagnosis cannot be reached. We reviewed our experience in this category to identify useful diagnostic parameters. Twenty-four such FNAs with surgical follow-up were retrieved from AUBMC files (2003-2009). Cytology slides were reviewed blindly. All cases were females, 29-73 years. There were three erroneous and 21 inconclusive diagnoses. The majority (15) was invasive adenocarcinomas: two cribriform, four tubular, one lobular, and eight not otherwise specified. The remaining cases were papillary and fibroepithelial tumors (three each), ductal carcinoma in situ, cribriform (two), and one adenomyoepithelioma (AME). Useful diagnostic features included: (1) Biphasic cell population with focal nuclear atypia and intranuclear and cytoplasmic vacuolar inclusions (AME). (2) Complex clusters of epithelial cells with cribriform architecture (cribriform carcinoma). (3) Rigid tubular epithelial structures with abrupt change in diameter, ending in pointed tips with abnormal branching (tubular carcinoma). (4) Cellular stromal fragments (fibroepithelial tumors). (5) Papillary fibrovascular cores, columnar cells, and three-dimensional papillary epithelial fragments (papillary tumors). Myoepithelial cells classically described in benign aspirates were not always a discriminatory factor. The "gray zone" in breast FNA is usually due to overlapping cytologic features of some benign and malignant lesions. Useful distinguishing cytologic features are described.