Early identification of circulating neuroendocrine tumour cells by flow cytometry prior to surgical diagnosis

moderate co-expression of CD200 (top row, grey dots).This population lacked expression of CD34, CD38, B-lymphoid markers CD19 and CD20; T-lymphoid markers CD3, CD4, CD5, CD7 and CD8; and myeloid markers CD13, CD33 and CD117.This immunoprofile was suggestive of circulating tumour cells from a neuroendocrine neoplasm.Reflex flow cytometric analysis showed co-expression of epithelial cell adhesion molecule (EpCAM, also known as CD326) (middle row, black dots) confirming an epithelial malignancy.The peripheral blood film was retrospectively reviewed, and rare abnormal large cells with a high nuclear to cytoplasmic ratio, fine chromatin and small nucleoli were identified (bottom row, Wright's stain, x60 objective lens).Biopsy of the right hilar mass confirmed a small cell carcinoma positive for pan-cytokeratin (patchy) and synaptophysin (patchy).The pathology report was finalised 2 days after the circulating tumour cells were identified by flow cytometry.Flow cytometry can be used for the identification of nonhaematopoietic malignancy in serosal fluid, lymph node and bone marrow. 1 EpCAM is the most commonly used marker for this purpose. 1Neuroendocrine neoplasms share a common immunophenotype (CD56-bright, CD45-negative, CD200-positive) that can be easily detected by conventional leukaemia/lymphoma panels 1,2 even in the absence of EpCAM staining.While uncommon, circulating tumour cells can be identified by flow cytometry, even prior to surgical diagnosis.