Improved enrichment of circulating tumor cells from diagnostic leukapheresis product.

The median number of circulating tumor cells (CTCs) detected in 7.5 mL of peripheral blood by CellSearch (PB-CS) in patients with metastatic prostate cancer is in the order of 1-10, which means many samples have insufficient tumor cells for comprehensive characterization. A significant increase is obtained through Diagnostic LeukApheresis (DLA), however, only 2-3% of the DLA product can be processed per CellSearch test, limiting the gain. We processed aliquots from 30 DLA products of metastatic prostate cancer patients consisting of 0.2·10 9 leukocytes using CellSearch (DLA-CS) as well as the newly introduced Reduced Enrichment Reagent protocol (RER), which uses 10-fold less enrichment reagents than DLA-CS. The number of tumor cells and the total number of captured cells were determined using the CellTracks Analyzer. Additionally, for six DLA samples, a 1.0·10 9 leukocyte aliquot was processed (RER+), using 2-fold less enrichment reagents than DLA-CS. A median 2.7-fold reduction in leukocyte co-enrichment was found between DLA-CS and RER methods without any loss in tumor cell recovery (Wilcoxon Signed Ranks Test, p=0.953. Using 1.0·10 9 leukocyte aliquots a 4-fold increase in tumor cells was found compared to DLA-CS and a 19-fold increase compared to PB-CS was obtained. The here-introduced RER protocol results in a higher final sample purity without any loss in tumor cell recovery while using 10-fold less CellSearch capture reagent. With this improved method, 26% of the leukapheresis sample can now be processed using reagents from a single CellSearch test, enabling the obtainment of a sufficient number of CTC for comprehensive characterization in most metastatic prostate cancer patients. This article is protected by copyright. All rights reserved.