Some common lesion leading to false positive diagnosis in FNA of breast are listed with Keys to differentiate them. Artifactual Atypia Most common of these is disruption of cell aggregates by too vigorous smearing, which can mimic the loss of cohesion characteristic of malignant epithelial cells . Excessive smearing pressure can also cause smudging of nuclei, giving a false impression of nuclear enlargement and pleomorphism. Dying artifacts in alcohol-fixed Pap smears have a similar effect.
Hormonal Stimulation and Physiologic :Hyperplasia in Pregnancy and Lactation Physiologic hyperplasia of acinar epithelial cells in late pregnancy and lactation can look worrying in FNA smears. Key: The recognition of milky secretion is the main clue to a correct diagnosis to be correlated with clinical information.
Reactive Atypia This is seen in mastitis fat necrosis, postoperative repair, and post radiation. Key:Correct clinical information is important. A history of previous tissue injury and the presence of acute inflammatory cells (not just lymphocytes) rarely seen in breast cancer call for caution and careful evaluation of the nuclear structure of atypical cells.
Fibroadenoma Epithelial atypia, most likely hormone related, can be prominent in smears of fibroadenoma. This is the most frequent cause of false positive diagnosis in breast FNA. Key: In most cases, the atypical cells constitute only a minor part of the cell population. The presence of benign components is a safeguard against an erroneous malignant diagnosis.
Papillary Lesions The combination of high cellularity, loss of cell cohesion, and variable nuclear atypia sometimes seen in smears from benign papillary lesions may raise a suspicion of malignancy. A false positive diagnosis is possible, particularly if a papillary microarchitectureis notidentified. Key: In general, the presence of background apocrine cells, foam cells, and single bipolar nuclei suggest a benign papilloma. REFERENCES 1. Franze´n S, Zajicek J. Aspiration biopsy in diagnosis of palpable lesions of the breast. Acta Radiol. 1968;7:241–262. 2. Zajdela A, Ghossein NA, Pilleron JP, et al. The value of aspiration cytology in the diagnosis of breast cancer: experience at the Foundation Curie. Cancer. 1975;35:499–506. 3. Greenberg M. Diagnostic pitfalls in the cytological interpretation of breast cancer. Pathology. 1996;28:113–121.