Recently, PGRMC1 has been identified as a putative binding protein for sigma-2 ligands,(58) which exhibit an anti-cancer effect and various pathological effects in the nervous system.(59) We have shown that the sigma-2 ligand DTG is able to bind to the heme-stacking dimer of PGRMC1, but the binding affinity is very low (Kd = 84 μM), indicating that PGRMC1 is not the sigma 2 receptor.(60) In addition, TMEM97 was identified as a putative candidate for the sigma 2 receptor with high binding affinity.(61) However, the function of TMEM97 remains unclear. Here, AP2S1 is linked to cancer.