<p>In (a-b) we analyzed the effect of freezing, storage at -80°C and thawing by qPCR array on the expression of 64 genes of NB cells spiked into PB. In (a) we show the effect when after thawing the samples were only enriched by magnetic bead-based separation, whereas in (b) we introduced an additional density gradient separation prior to magnetic bead-based separation. Red dots represent genes that are significantly changed (p<0.05, |log<sub>2</sub>FC|>1) at given conditions compared to the baseline (LAN-1 cells enriched and homogenized in TRIzol immediately after spiking). Genes with |log<sub>2</sub>FC|>1 and p>0.05 are represented by black dots (not significant), as their expression was not coherently changed between the three biological replicates. The log<sub>2</sub> fold change is indicated on the y-axis and the mean Ct values in the x-axis. In (c-d) we analyzed the same effects on NB cells spiked into BM by microarrays. The mean log<sub>2</sub> expression is shown in the x-axis, and the log<sub>2</sub> fold change on the y-axis.</p
