Detection of micrometastases by flow cytometry in sentinel lymph nodes from patients with renal tumours

BACKGROUND: Stage is an important prognostic factor in renal tumours and dissemination to regional lymph nodes is associated with poor outcomes. Lymph nodes are routinely assessed by immunohistochemistry and microscopic evaluation, a time-consuming process where micrometastases might go undiagnosed. We evaluate an alternative method for detecting metastatic cells in sentinel nodes (SNs) by flow cytometry. METHODS: A total of 15 nodes from 5 patients diagnosed with renal tumours were analysed by flow cytometry. Staining for the intracellular marker cytokeratin 18 (CK18) with the surface markers carbonic anhydrase IX (CA9) and Cadherin 6 were used in flow cytometry analysis. Peripheral blood mononuclear cells (PBMCs) with the addition of known concentrations of cancer cell lines were analysed to investigate the sensitivity of micrometastasis detection. RESULTS: Stability of the assay was marked by low intra-assay variability (coefficient of variance ⩽16%) and low inter-assay variability (R(2)=0.9996–1). Eight nodes in four patients were positive for metastasis; six of them were considered being micrometastatic. These metastases were undetected by routine pathology and the patients were restaged from pN0 to pN1. CONCLUSIONS: Flow cytometry is able to detect micrometastases in lymph nodes of renal tumour patients that were undetected under H&E examination.