Some propstate cancers are fast growing; others grow more slowly. Researchers with the Memorial Sloan-Kettering Cancer Center and the Howard Hughe Medical Institute in New York say that testing tumor cells for a specific protien may help identify the aggressive cancers earlier.
The protien p27 is abundant in normal prostate, says Sloan-Kettering's Dr. Carlos Cordon-Cardo. (p27 is different from another protien, PSA, or prostate specific antigen, often measured to warn of cancer.) "p27 is like on a car," explains cordon-Cardo. "It stops cells from proliferating." Now, ananlyzing 130 prostate-cancer specimens, Cordon-Carlo's team has found that on the whole, cancers with lower levels of p27 grew and spread more rapidly, whereas those with higher p27 were less aggressive.
If long term studies determine that measuring p27 accurately prdict the course that prostate cancer will take, says Cordon-Carlo, "we could tailor therapy for each patient and improve the chances for a cure."
PSA is a glycoprotien (part carbohydrate, part protien) normally found in the cytoplasm of prostatic cells. This antigen can be detected in all males. However, its level is greatly increased in patients who have prostate cancer. Although PSA was originally measured by histochemical techniqes, radioimmunoassay (RIA) techniques have recently increased its accuracy.
Elevated PSA levels are associated with prostate cancer. The higher the levels, the greater the tumor burden. Further, the PSA assay is a sensitive test for monitoring response to therapy. Successful surgery, radiation, or hormone therapy is associated with a marked reduction in the PSA blood levels. Subsequent significant elevation in PSA indicates the recurrence of prostate cancer.
PSA is more sensitive and specific than other pratatic tumor markers, such as prostatic acid phosphatease (PAP).
The enzyme acid phosphatase, often reffered to as prastatic acid phosphatase, is found in highest concentrations in the prostate gland. The determination of PAP is primarilly used to diagnose and stage prostatic cancer and to monitor the results of treatment. Elevated levels are seen in patients with prostatic cancer that has metastasized (started spreading) beyond the capsule to other parts of the body, especially the bone. If the tumor is succsessfully treated by surgery, PAP levels decrease in several days. If the tumor is treated by estrogen therapy, enzyme levels return to normal in several weeks. Rising levels of PSA may indicate a poor prognosis. PSA is also found in high concentrations in seminal fluid. For this reason, PSA tests may be done on vaginal secretions to investigate alleged acts of rape.
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