FOR IMMEDIATE RELEASE
May 13, 1998
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Laurie Slothower
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STUDY SUGGESTS BCL-2 GENE AS CAUSE FOR AGGRESSIVE PROSTATE CANCER IN AFRICAN AMERICAN MEN
Findings underscore need for early screenings to reduce mortality in this ethnic group.
(SACRAMENTO, Calif.) -- A gene that blocks cells from dying may play a role in prostate cancer in African Americans, offering a new hypothesis as to why black men have the highest rate of prostate cancer in the world. The findings appear in the June issue of the Journal of Urology.
"African-American men develop prostate cancer earlier and in a more aggressive form than any other ethnic group," says Ralph W. deVere White, director of the UC Davis Cancer Center and lead author of the Journal of Urology study. "They are more likely to die from the disease and more frequently have a recurrence after treatment with radical prostatectomy, the surgical removal of the prostate gland. Even when consideration is given to diet, lifestyle, or socioeconomic factors, the differences in the behavior of prostate cancer between the races remains unexplained."
But collaborative research done at UC Davis School of Medicine and Medical Center, Howard University in Washington, D.C., and the Northern California Cancer Center in Union City, Calif., suggests that the difference in prostate cancer pathophysiology in African Americans may lie in altered expression of bcl-2, a gene that plays a central role in preventing cells from dying.
In all cells, a series of genes plays an integrated role in allowing the cell to progress through the cell cycle, DNA replication, and cell division. At the same time, a separate set of genes, interrelated with those that govern the cell cycle, work to allow the cell to enter programmed cell death, or apoptosis, at the appropriate time.
This can occur as a natural part of cell aging, or in response to DNA damage. Cancers can grow either by an increase in proliferation, a decrease in apoptosis, or both. In prostate cancer, the gene bcl-2 acts as a major block to cell death.
In the Journal of Urology study, the researchers evaluated four markers of tumor aggressiveness in cancerous prostates removed from 43 black and 74 Caucasian men to determine which factors were related to racial differences. The markers include:
-- DNA ploidy, the number of extra chromosomes in the nucleus
-- proliferation, the degree of tumor growth
-- p53, a gene that is overexpressed in many cancers and predicts tumor progression
-- bcl-2, a gene that blocks cell death
While no significant differences in levels were found in three of the four markers in these two groups of men, the researchers found a connection between bcl-2 levels and the more aggressive tumors found in the prostates removed from black men. They also found both low-and high-grade black prostate tumors had similar DNA ploidy distributions, rather than a higher degree of abnormality for the high-grade tumors as would be expected.
"Our studies suggest that in African Americans, tumor growth is more rapid because fewer cells are instructed to die," says deVere White. "With the bcl-2 gene overexpressed, it causes prostate cancer cells to flourish when they would normally perish. And because the chances that a prostate cancer tumor will metastasize increases with tumor size, it makes sense that if programmed cell death is blocked, metastasis could occur earlier in the course of the disease."
Drs. deVere White and Aaron Jackson, Chief of the Division of Urology at Howard University and a co-author of the study, say that more study is needed to determine the significance of bcl-2 and how it interacts with other genes.
Yet, since this study helps to explain why cancers occur earlier and more aggressively in African American men, it also underscores the importance of screening measures in this ethnic group, says Jackson.
More than 300,000 men are diagnosed with prostate cancer each year, and more than 40,000 will die from the disease. Warning signs for prostate cancer include inability to urinate, blood in the urine, and pain or burning during urination. In its beginning stages, however, prostate cancer has no symptoms.
"In its early stages, prostate cancer is silent," says Dr. Jackson. "A person cannot make a diagnosis of prostate cancer on themselves based on symptoms." As a result, Howard recommends that African American men and those who have a family history of prostate cancer undergo a physical exam and a prostate-specific antigen (PSA) test when they turn 40, with regular checks every year thereafter.
The encouraging news from the study, says deVere White, is that "if these cancers are detected while they are very small, there is no difference in survival rates between black and whites. And the overall cure rate for prostate cancer caught in its earliest stages is greater than 90 percent."
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This research was supported by a public health grant from the National Institutes of Health.
To learn more about prostate cancer and African American men, visit these Web sites:
The UC Davis Cancer Center http://cancer.ucdmc.ucdavis.edu/prostate.htm
The American Cancer Society: 1998 Facts and Figures
http://www.cancer.org/bottomsearch.html
CancerNet at the National Cancer Institute
http://cancernet.nci.nih.gov
OncoLink at the University of Pennsylvania
http://www.oncolink.upenn.edu
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