Lee and colleagues used serial analysis of gene expression (SAGE) to analyze the effect of RFR on gene expression at the genome level i.e. they examined the effect on a large number of genes at the same time. The authors exposed human HL-60 cells to pulsed RFR at 2.45 GHz frequency at an average SAR of 10 W/kg for 2 hours and 6 hours. They found that in the 2 hour exposure, 221 genes altered their expression, and 759 did so after 6 hours exposure. Most of the genes altered in the 2 hour exposure were not amongst those altered in the 6 hour exposure. In the 6 hour exposure the upregulated genes included those relating to apoptosis, while the downregulated genes included cell cycle genes. No significant increase was observed in the expression of heat shock genes, which the authors believe is a sign that the observed effects on other genes were not due to thermal effects.