Expression of P2Y12R in cancer cells has been poorly investigated. The receptor protein has been found in glioma and astrocytoma cells (Jin et al., 2001; Czajkowski et al., 2002; Burnstock and Di Virgilio, 2013) where it has been reported to increase cancer cell proliferation. In basal condition, C6 glioma cells expressed predominantly P2Y1 mRNA with lower levels of P2Y12 mRNA, but, when the cells were cultured in serum-free medium, the expression of P2Y1 mRNA decreased, whereas that of P2Y12 significantly increased (Czajkowski et al., 2004). In these conditions, ADP enhanced ERK1/2 phosphorylation and PI3K signaling by activating the P2Y12R (Czajkowski et al., 2004).