Results recently published in theJournal of the National Cancer Institute indicate that the protein prostasin may serve as an effective screening marker for ovarian cancer, particularly when combined with CA 125.
Ovarian cancer is the most lethal gynecological cancer and is the fifth leading cause of cancer death in U.S. women. Because epithelial ovarian cancers begin deep in the pelvis, they often do not cause any symptoms until they are at an advanced stage. Women diagnosed with early stage ovarian cancer have an average survival rate of 90% after 5 years (depending on the aggressiveness of the cancer); however, women diagnosed in advanced stages only have a 28% survival rate after 5 years. The lack of effective treatment for late stage ovarian cancer and the difficulty in diagnosing early stage ovarian cancer demonstrate the need for an accurate biomarker.
A biomarker is a biological substance sometimes found at elevated levels in the blood, other bodily fluids or tissues. Biomarkers are specific to particular types of cancer and are valuable because they signal the possible presence of cancer before severe symptoms arise. CA 125 is the standard biomarker utilized to diagnose and/or monitor ovarian cancer. Researchers have been trying to find more associations between particular elevated biomarkers and specific cancers for clinical use.
Through laboratory processes, researchers recently discovered a gene that is over-expressed in ovarian cancer cells. This gene produces a protein called prostasin that is released into the blood. To determine the clinical utility of prostasin as a biomarker for ovarian cancer, researchers evaluated prostasin levels from the blood of 64 patients who had been diagnosed with ovarian cancer and 137 patients who did not have ovarian cancer. Patients with ovarian cancer had higher prostasin levels in their blood compared with patients who did not have ovarian cancer. Additionally, 14 of 16 patients with ovarian cancer who had surgery to remove the cancer experienced a significant drop in prostasin levels following surgery. Patients with stage II ovarian cancer had the highest blood levels of prostasin, indicating that prostasin may be effective in detecting early stage ovarian cancers. However, patients with a type of ovarian cancer called mucinous ovarian cancer appeared to have lower levels of prostasin than patients with other types of ovarian cancer.
The study also examined blood from 37 patients with nonmucinous ovarian cancer and 100 patients with no ovarian cancer to determine if CA 125 and prostasin are complementary biomarkers for ovarian cancer. Together, CA 125 and prostasin correctly identified patients without ovarian cancer 94% of the time and correctly identified patients with ovarian cancer 92% of the time. In contrast, CA 125 alone only correctly identified 64.9% of patients with ovarian cancer and prostasin alone only identified 51.4% of patients with ovarian cancer; however, CA 125 alone and prostasin alone correctly identified patients without cancer 94% of the time.
In conclusion, these results suggest that prostasin has clinical potential as a biomarker for ovarian cancer, particularly when results are combined with CA 125. Researchers are hopeful that the use of these biomarkers can translate into earlier detection and treatment for ovarian cancer, with the goal of ultimately improving survival for patients with this disease. Patients being tested or monitored for ovarian cancer may wish to speak with their physician about participating in a clinical trial further evaluating prostasin. (Journal of the National Cancer Institute, Vol 93, No 19, pp 1458-1464, 2001)