You may recall that one of the desired characteristics of an ideal tumor marker is to correlate with tumor mass and degree of metastasis. In this respect, PSA serves as an effective tool to help assess the stage of prostate cancer. Higher PSA levels strongly correlate with tumor mass and metastasis. PSA levels greater than 50 µg/L are highly indicative of an advanced stage of prostate cancer. Similarly, patients with less than 20 µg/L of PSA seldom have bone metastases.2
