To further examine the early instructive role of NK cells in the initiation of cancer immunity and to validate our findings in a setting independent of CRISPR mutant cells, we took advantage of genetically engineered mice lacking EP2 and EP4 receptors (encoded by Ptger2 and Ptger4), which mediate the downstream immunomodulatory signaling of PGE2 (Kalinski, 2012). The gene discussed is PTGER4; the disease is cancer.