CXCR4 and cancer: In contrast to BP-NEN, a positive association was found in GEP-NEN between GPER and Ki-67 expression (rsp = 0.281; p < 0.001) and between GPER expression and the expression of typical markers associated with a negative prognosis for cancer, including the chemokine receptor CXCR4 (rsp = 0.191; p = 0.013) and PD-L1 (rsp = 0.212; p = 0.006), whereas there was a negative correlation with CgA, which is associated with a good prognosis for GEP-NEN (rsp = −0.159; p = 0.040) [30,32].