Alveolar Macrophages Mimic Tumor Cells in Lung Tissue: A Diagnostic Pitfall in Cytology FNA and EBUS Specimens

Fine-needle aspiration (FNA) or core needle biopsy via EBUS procedure is commonly used to assess suspicious lung nodules. Alveolar macrophages are commonly seen in these specimens. In cases when hypercellular specimens with large aggregates of alveolar macrophages are encountered, especially when they show epithelioid morphology, vacuolated cytoplasm, and significant cytological atypia, including marked anisonucleosis and intracytoplasmic inclusion, they can be mistakenly interpreted as "lesional cells" during rapid on-site evaluation (ROSE) and cease the EBUS procedure prematurely. It is important to keep in mind that epithelioid alveolar macrophages may mimic lung neuroendocrine tumor (NET), lung adenocarcinoma, or even metastatic process. Cytoplasmic pigmentation and immunohistochemistry analysis can be extremely useful to prevent a false diagnosis of malignancy.