April 2, 2000 (AARC, San Francisco) -- A new test show promising results in predicting which men are at high risk for metastatic prostate cancer and, who therefore, may be candidates for early systemic treatment, before the disease takes hold in other sites.
For more than 50 percent of men diagnosed with locally confined prostate cancer, the disease later spreads. Clinicians rely on tumor classifications based on a spectrum of "histologic grades" to guide treatment decisions.
At diagnosis, however, most prostate cancers are "moderately differentiated" -- meaning that they don't yet display the distinguishing features that help determine appropriate therapy. If clinicians could foresee which prostate cancers would metastasize, they could recommend therapies designed for nomadic malignant cells and spare other patients the effects of unnecessary treatment.
A protein called thymosin ß15 (T beta 15) may predict spread of the disease. According to researchers who investigated it, the substance showed a high degree of accuracy as an early warning signal for metastasis. TB15 is thought to enhance the metastatic potential of prostate cancer cells.
A research team at Massachusetts General Hospital and Harvard Medical School in Boston examined Tß15 in biopsy specimens from 32 men with clinically localized, moderately differentiated prostate cancers who were treated only with radiation therapy, not surgery or chemotherapy. They followed the men for a period of six years.
They scored the staining intensity of Tß15 from 3+ (the strongest) to 1+ (the weakest). Of the patients whose initial biopsy specimens stained 3+, 63 percent experienced spread of their prostate cancer to bone, and 75 percent of men with + scores showed elevated prostate-specific antigen (PSA) within five years. Rising PSA levels are currently used to determine if the disease has spread -- probably to the bone, the most common metastatic site in prostate cancer.
"If a larger study supports our results, a low-cost Tß15 test can be used at initial diagnosis to advise patients on the potential need for systemic therapy, which is the only curative treatment for clinically occult, micrometastatic disease," said Arnab Chakravarti, M.D., Harvard Medical School. "The same test may help patients decide against radical local treatment, such as surgery, if they show a low probability of distant failure."
Dr. Chakravarti and his research team are the principal investigators for the multi-institutional Radiation Therapy Oncology Group, which will conduct a larger, two-part study involving approximately 100 patients who will be monitored for 10-15 years. The first study will examine Tß15 in moderately differentiated prostate cancers: the second study will broaden to a larger range of histologic grades.
"Thymosin ß15 Predicts for Distant Failure in Patients with Clinically Localized Prostate Cancer" (Abstract #4070)
Arnab Chakravarti, E.M. Zehr, A.L. Zeitman, W.U. Shipley, W.B. Goggins, D.M. Finkelstein, R.H. Young, and C.L. Wu was given as a
Poster Session on April 4, 2000 at the Annual Meeting the American Association for Cancer reearch (AACR) in San Francisco.