The reviewed cases emphasize the concept that negative immunohistochemical staining for PSA or ACTH should not exclude an ectopic ACTH-secreting prostate neuroendocrine tumor as this subtype of PCa usually loses or partially expresses PSA, as it is reported that up to 30% of ACTH-secreting tumors stain negative for ACTH [10,17,19,20,21,27,33,34]. The gene discussed is KLK3; the disease is prostate neuroendocrine neoplasm.