If cancer is present, the level of PSA in the blood rises as the tumour grows. PSA can be particularly useful after a diagnosis as a guide to how far the cancer has grown. This is called staging. Lower levels of PSA are found in association with small tumours that may be still confined to the prostate gland (localised). PSA levels of 10 ng/mL or less have the best chance of being localised. The PSA level and the cancerous characteristics of the tumour cells themselves (called grade or Gleason score) can indicate the risk that a tumour has grown beyond the prostate. This is important because curative treatment is most successful if the cancer is confined to the prostate.