A roadmap for a comprehensive diagnostic approach to fine needle cytology of lymph node metastases.

Fine needle cytology (FNC) is widely used as a first-line procedure in the diagnostic algorithm of lymphadenopathies. In a metastatic setting, a first-line diagnostic approach identifies non-haematopoietic malignancy; however, cytopathologists could also provide a second diagnostic level, identifying the origin of the primary tumour. This paper outlines a comprehensive and practical approach to the cytological diagnosis of lymph node metastases. Cytological diagnoses of lymph node metastases performed over a 10-year period were selected and divided into two groups. The first group, labelled "oncological," comprised patients with a previous history of malignancy; the second group, labelled "naïve," included patients with no relevant history. Pathology records were retrieved to record microscopic findings, namely, background appearance, group architecture, and specific cell features; data from cell block (CB) preparations were also collected. Overall, 982 cases were selected: 497 cases (50.61%) in the naïve group, and 485 (49.39%) in the oncological group. Overall, a second diagnostic level was achieved in 834/982 cases (84.92%); cases diagnosed as carcinoma not otherwise specified were more frequent in the naïve group than in the oncological group (17.51% vs. 8.04%, P < 0.01). Notably, although CB material was available in only 44.87% of the naïve cases, we were able to achieve a second diagnostic level thanks to the integration of clinical and cytomorphological findings, plus lymph node topography, in 82.49% of the cases. Our results confirmed that in a metastatic setting, FNC can reliably lead to the identification of the origin of the primary tumour.

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© 2022 The Authors. Cytopathology published by John Wiley & Sons Ltd.