<p><b>(a)</b> We spiked LAN-1 NB cells into fresh PB and kept the samples for 0, 24, 48 and 72h at room temperature and, for the same time periods, at 4°C prior to density gradient separation. The LAN-1 cells were enriched from the MNC fraction with magnetic beads to a 99% purity of the tumor cell fractions prior to homogenization in TRIzol. RNA was isolated from all seven samples simultaneously and used for the qPCR array. (<b>b)</b> LAN-1 cells were spiked into PB and tumor-free BM, and density gradient separation was immediately performed. The MNCs were frozen in 20% DMSO for seven days at -80°C. After thawing, the LAN-1 cells were either directly enriched by magnetic bead-based separation, or an additional density gradient separation (*) was performed prior to magnetic bead-based separation. The samples were homogenized in TRIzol and the isolated RNA was used for qPCR (in case of PB) and microarrays (in case of BM). <b>(c)</b> LAN-1 cells were spiked into PB and density gradient separation of MNCs was performed without delay, following two enrichment steps in a row. The >99% LAN-1 cell fractions were homogenized in TRIzol and RNA was isolated from all samples simultaneously. qPCR arrays were performed in order to analyze the effect of enrichment on selected genes.</p
