Fine needle aspiration (FNA) of the breast is a well-tolerated procedure used to evaluate palpable breast masses, has a reported mean specificity of 99%, and a reported sensitivity of 70-99%. The false positive rate vanes from 04.4% in most larger series, with a reported false negative rate rangng from 0.7-22%; however, higher false negative rates have been reported in tumors under 2 cm in diameter. The FNA technique uses a fine, 20 gauge or less, needle and is not associated with a significant risk of tumor growing out the needle tract.
FNA cytology is not effectively used if a breast mass cannot be palpated or distinguished from fibrous tissue within the breast. The procedure can be applied to nonpalpable masses detected by mammography by employing stereotactic techniques. The cytologic samples obtained from FNA can be used to distinguish atypical ductal hyperplasia from in situ or invasive ductal carcinoma; however, cytologic criteria to effectively distinguish ductal carcinoma in situ (XIS) from invasive adenocarcinoma are not definitive in many cases, and are dependent on variables related to the type of intraductal tumor, the size and character of the cell groups, and the presence of single or disaggregated tumor cells.
Employing current cytologic criteria, lobular carcinoma in situ (LCIS) may be distinguished from invasive lobular carcinoma in some cases; however, the individual LCIS cells are not morphologically distinct from lobular carcinoma cells. Atypical lobular hyperplasia has cellular features essentially the same as those seen in LCIS.
Needle biopsy (NB) employs larger needles of 14-16 gauge. Stereotactic guidance for NB can be augmented with cytopathology by preceding the biopsy with FNA, and/or by collecting the cellular sample available when washing the needle after the tissue sample is removed. These needle biopsy washings are often highly cellular and are complementary to the tissue diagnosis.
FNA samples or NBs, if adequately cellular, are applicable for DNA analysis by static image analysis (flow cytometry). Flow cytometry is of limited practical value where cellularity or tumor representation is poor because morphologic confirmation cannot be established. These samples can also be used to calculate tumor proliferative fraction, employing Ki-67 antigen. Quantitation of nuclear organizer (AgNOR) regions and expression of HER-2/neu and p53 proteins can be accomplished in these samples; estrogen and progesterone receptors can also be detected and quantitated.