Neuroendocrine carcinomas: Cytological mimics and diagnostic dilemmas

Background: Neuroendocrine carcinomas (NEC) are rare tumours with multiple morphologic mimics. The cytologist may miss these cases if not aware.

Aims and objects: We focused upon the clinical presentation, cytological features and problems in the diagnosis of NEC.

Materials and methods: We studied the detailed cytomorphology of 19 cases of NEC (histopathology proved).

Results: Of these 19 cases of NEC, 15 cases constituted fine needle aspiration (FNA) specimens, one transbronchial needle aspiration specimen, two pleural fluid specimens and a single biliary brushing specimen. All of the FNA specimens were from extra-pulmonary sites (namely, breast, pancreas, liver and three lymph node FNAs). Eight of the 19 cases (42.1%) showed a significant disparity between cytological and histopathology diagnoses. The break-up of discordant diagnoses are of adenocarcinoma (three cases), Ewing's sarcoma (one case), infiltrating ductal carcinoma (one case), lymphoma (one case), and squamous cell carcinoma (two cases). The cytology of NECs predominantly showed discrete, round to oval cells with a moderate amount of cytoplasm. The nuclei were pleomorphic, having prominent nucleoli. Occasional cases showed characteristic salt and pepper chromatin and were correctly diagnosed as a neuroendocrine group of tumours.

Conclusion: The accurate diagnosis of NEC depends on clinical correlation, meticulous screening for any obvious neuroendocrine features and cell block morphology. Immunohistochemistry is essential for ruling out of tumours of neuroendocrine origin. A Ki67 index is mandatory for grading of all neuroendocrine tumours.