P2RY2 and neoplasm: Among the receptors engaged by extracellular ATP (P2 receptors), the P2Y2R is most consistently expressed (or overexpressed) by tumor cells, and it mediates proliferation in many tumors, for example, melanoma [9], lung [10], bladder [11] and prostate cancer [12]; however, controversial phenomena have also been reported in other tumor types, for example, esophageal [13], colorectal [14] and ovarian cancer [15].