The diagnosis of breast cancer is often made by fine-needle aspiration cytology (FNAC). Over a 4-year period, there were 1104 cases reported as carcinoma by FNAC at the Royal Marsden Hospital and in four of these the diagnosis was subsequently proven to be benign. This is an incidence of 0.36% and represents a positive predictive value in the series of 99.6%. The benign conditions that led to false positive cytodiagnosis were radiation-induced changes, granulomatous mastitis, and fibroadenoma. Although the reliability of FNAC of breast is high, clinicians should be aware of the limitations and pitfalls.
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