The ABCs About PSAs

Researchers at Duke Cancer Institute believe they have pinpointed why PSA (prostate-specific antigen) levels reflect cancer progression.

PSA is used as a screening tool for prostate cancer and as a marker of disease progression through a blood test.  PSA is present in small quantities in all men, but an increased amount should be considered suspicious for prostate cancer.  Researchers now think they've found a reason why increasing PSA means that a prostate cancer is growing.

Using human prostate cancer cells in a laboratory culture, researchers found that an antibody reacts with a cell-surface receptor (GRP78) on cancer cells to produce more prostate-specific antigen (PSA). The PSA arises from and then moves out of the cancer cell, where it can bind with the same antibody, (alpha2-macroglobulin or α2M) that caused its release from the cancer cell. The PSA then forms a complex with the antibody that also binds to the GRP78 receptor. This interaction activates several key pathways that cause cancer cell growth, cell movement and block cell death.

Senior author Sal Pizzo, M.D., Ph.D., chair of the Duke Department of Pathology said the use of PSA to make an initial diagnosis of prostate cancer has become controversial, but thinks PSA serves more usefully as a marker of progression, "particularly with a baseline value on record at the time of the original therapy."

All men should start screening for prostate cancer at age 50 primarily with a digital rectal exam performed by their primary care physician.  PSA screening can be used in conjunction with this if the physician feels that it is warranted.

Prostate cancer is the most commonly diagnosed cancer in American men. About 217,730 new cases of prostate cancer will be diagnosed this year, according to the American Cancer Society.