The mean activity (ΔF/min) was 2.3-fold greater in 3xCR than in GPC6 brains during slow, but not fast, expansion (p = 0.008 and p = 0.15, respectively, WR test), indicating an unexpected shortage of overall synaptic and somatic activity in GPC6 mice during slow tumor expansion. This evidence concerns the gene GPC6 and neoplasm.