By Catherine Arnst There's a commonly held belief in the U.S. that early detection of cancer saves lives. Consider the simple blood test for prostate cancer administered to millions of American men since the late 1980s. Widespread use of the PSA test -- which spots a telltale protein called prostate-specific antigen -- seems to bear out the early-detection theory.
Indeed, the American Cancer Society's annual report on cancer in the U.S., released on June 3, found that death rates have decreased by 1.1% a year for all cancers since 1993. But the biggest gains for cancer survivors have been registered for prostate cancer: From 1995 to 2000, the report says, 99% of prostate-cancer victims were still alive five years after diagnosis, vs. 70% in the mid-1970s.
The ACS is also very careful to point out, however, that the improvement is likely due to better treatment, and not widespread screening for prostate cancer. In fact, the PSA test has been controversial among cancer specialists for years, because it's wildly inaccurate -- it carries a 75% false-positive rating -- and there's little or no evidence that widespread use correlates with lower mortality rates. The ACS doesn't even recommend that men get routine PSA tests, nor does any other medical-standards body in the U.S.
New, more accurate tests for prostate cancer are under development, with one due out this month, but far more money and research has been poured into finding treatments for the disease than a test for it. The huge American Society of Clinical Oncology (ASCO) meeting taking place in New Orleans June 5-9 will bear this out.
"URGENT NEED." This premier showcase for new cancer research will presentore than 9,000 studies,but those focusingon detection take up less then half a page in the program index. "We need to recognize that PSA is no longer a marker for prostate cancer," Dr. Thomas Stanley, professor of urology at Stanford University School of medicine, told a recent medical conference. "We urgently need to find a new marker."
Prostate cancer certainly merits the attention. The ACS estimates that prostate cancer will be diagnosed in some 230,000 U.S. men this year, and 30,000 will die from it, making it the second largest cancer killer for men after lung cancer.
Why is the ACS so reluctant to embrace the test? Several large studies have found no difference in survival rates for prostate cancer between groups of men who routinely underwent PSA testing and those who did not. Also, many prostate tumors are so slow-growing that the patient might be better off if the tumors were left untreated.
FAILING GRADES. Dr. Otis Brawley, professor of oncology at Emory University's Winship Cancer Institute and a longtime critic of the PSA test, points to an NCI study that found that 12.2% of men aged 65 and over had a positive PSA test, but only 3% of men in that age group die from the disease. "That means three out of four men with localized prostate cancer would have grown old and died of something else," says Brawley. "That's a lot of overdiagnosis."
The problematic nature of the PSA test was highlighted by a National Cancer Institute (NCI) study published in the May 27 issue of The New England Journal of Medicine. The study found that the PSA test missed prostate cancer in 15% of men aged 62 to 91. What's more, 2% of those men had aggressive tumors when the tissue was examined after a biopsy.
Those results served to buttress the position of opponents of the test, who cite its inaccuracies. But proponents of the test cited the report as an argument for lowering the PSA threshold for further investigation of cancer, currently at 4 nanograms per milliliter of blood, to 2.5.
NEW REFINEMENTS. If the threshold were lowered, it could more than double the number of biopsies men in the U.S. undergo each year. About 1.2 million prostates are biopsied each year already, and only one out of every four turns up cancer. Although biopsies are usually safe, they can lead to bleeding and pain, cost several hundred dollars apiece, and often must be done more than once to confirm the presence of cancer. If cancer is found, even a very small tumor, the patient must make difficult decisions about treatment, which by itself can lead to impotence, incontinence, or even death. Several hundred men die each year from prostate surgery.
Most of the newer tests in development are refinements on the PSA test. Robert Getzenberg, a professor of urology at the University of Pittsburgh School of Medicine, has developed a screen for early prostate cancer antigen (EPCA), a subset of PSA that appears only when prostate tumors are present. In a study reported in May, the EPCA test accurately detected cancer in 90% of the tissue biopsies examined. An EPCA test that can be used on biopsied tissue will be marketed in June by Seattle's Tessera Diagnostics, and Getzenberg says a blood test is under development.
Such a test could go a long way toward improving cancer detection. But researchers complain that too few resources have been devoted to detection compared to treatment. Meanwhile, "I don't see the PSA test going away any time soon," says Dr. Mark Kawachi, director of the Prostate Cancer Center at City of Hope Hospital in Los Angeles.
Brawley says more men, and their doctors, should follow the recommendations of the ACS, which says doctors should "offer the PSA blood test" to healthy men at age 50 after discussing both the benefits and risks of testing. An educated patient could then decide for himself, based on his family history, age, and other risk factors, just how much testing he needs and wants. That may be the best advice until a more reliable test comes along. Arnst covers medicine and medical issues for BusinessWeek from New York