Starting from the cellular level, we investigated the Sig1R synthesis with Western blot and the accumulation of (S)-(−)- and (R)-(+)-[18F]fluspidine in the human prostatic cancer cells DU145 and PC3, as well as in the cell lines A431 and FaDu (squamous carcinoma), A375 (malignant melanoma), and U87-MG (glioblastoma). Here, SIGMAR1 is linked to prostate cancer.