The Ki-67 biomarker is a proliferation antigen that is detected by a process called immunohistochemical staining. When a tumor cell tests positive for Ki-67, the tumor is actively growing.
Prostate cancers typically have very low percentages of growing cells and they grow slowly. Pollack and others have previously shown in smaller studies that the greater the proportion of prostate tumor cells with Ki-67, the more aggressive the cancer. Prior studies involved small patient numbers and did not definitively establish the usefulness of the Ki-67 biomarker.
"Our study conclusively shows that Ki-67 was the most significant determinant of distant metastasis and death in prostate cancer patients," explained Pollack. "The relationship of Ki-67 to patient outcome is a continuous function, wherein the higher the percent of Ki-67, the greater the risk of an adverse result. In addition, Ki-67, along with PSA, Gleason score and stage, appears to be valuable in determining whether high-risk patients may be spared long-term androgen deprivation."
Pollack says that a consistent threshold for the application of Ki-67 on a routine basis has not been previously established. In this study, when greater than 7.1% of the tumor cells stained for Ki-67, there was a significantly increased risk of distant metastasis and death due to prostate cancer.
Furthermore, Pollack adds, Ki-67 should be very useful in stratifying patients in future clinical trials.
Other authors in the study include Michelle DeSilvio, American College Of Radiology, Philadelphia, Pa.; Li-Yan Khor, Fox Chase Cancer Center, Philadelphia, Pa.; Rile Li, Baylor School of Medicine, Houston, Tex.; Tahseen Al-Saleem, Fox Chase Cancer Center; M. Elizabeth Hammond, University of Utah School of Medicine, Salt Lake City; Varagur Venkatesan, Medical College of Wisconsin, Milwaukee; Roger Byhardt, University of California San Francisco, Calif.; Gerald E. Hanks, retired from Fox Chase Cancer Center; Mack Roach, University of Western Ontario, London, Ontario; William Shipley, Massachusetts General Hospital, Boston; and Howard Sandler, University of Michigan Medical Center, Ann Arbor.
Fox Chase Cancer Center, one of the nation's first comprehensive cancer centers designated by the National Cancer Institute in 1974, conducts basic, clinical, population and translational research; programs of prevention, detection and treatment of cancer; and community outreach. For more information about Fox Chase activities, visit the Center's web site at www.fccc.edu or call 1-888-FOX CHASE.