Some very early cancers can be felt on a rectal exam before they cause the PSA level to be elevated. Other cancers will elevate the PSA level before they can be detected on the rectal exam. To maximize the accuracy of screening, it’s best to have both the test and the examination. In addition, some high-grade or Neuroendocrine forms of prostate cancer do not produce much PSA. They can be detected on the DRE before the PSA becomes elevated.