GPER1 and endometrial cancer: GPER also mediates invasion by endometrial cancer cells through the stimulation of ERK pathway, as well as the increase of interleukin-6 secretion, leading to the production and activation of matrix metalloproteinases MMP-2 and MMP-9 known to degrade extracellular matrix components and to be involved in cancer invasion and metastasis (He et al., 2009, 2012; Du et al., 2012a).