More news on the subject of prostate cancer:
An intermediate PSA level of 2.5 -- 10 predicted cancer status correctly only half the time.
Within that PSA range, the antibody test was correct 94% of the time.
In all samples, the antibody test was 93% accurate in determining cancer status compared with 80% for the PSA test.
Potential Prostate Cancer Screening Tool Waits in the Wings 2
A New Approach To Cancer Screening a Promising Method for Detecting
Prostate Cancer Is More Precise Than PSA Test, Study Says
By CHARLES FORELLE
Staff Reporter of THE WALL STREET JOURNAL
September 22, 2005; Page D1
A newly developed screening method may significantly improve the detection of prostate cancer.
In a study today in the New England Journal of Medicine, the new method was found to be far more precise than the widely used PSA test.
Currently, to spot early signs of prostate cancer, doctors advise most men 50 or older to get an annual test for elevated blood levels of an enzyme called prostate-specific antigen. The problem is there is no clear way to divine what most results mean. Some men with low levels, in fact, turn out to have cancer. Some others with high levels have only a benign prostate enlargement or irritation. Although a very high PSA level is a strong warning sign for cancer, a reading in the middle is muddier.
Now, researchers at the University of Michigan and Harvard have developed a different kind of test that appears, in a small study, to be more accurate. It also points to a method of detection -- relying on the body's immune system for the vital clues that cancer is present -- that could be applied to other types of cancer. An approved test based on the method, which looks for particular antibodies in the blood, awaits broader clinical study and is likely years away. But its arrival would be significant.
A more accurate test for prostate cancer could not only improve early detection, but also spare men from unnecessary biopsies, the surgical removal of a prostate piece for testing, which is often prescribed if PSA levels are elevated. Often, biopsies are recommended for a PSA reading of four or higher, corresponding to four billionths of a gram of antigen per milliliter. But only about a quarter of men with PSA readings between four and 10 actually turn out to have cancer after a biopsy is performed.
This imprecision has long created dilemmas for men who fall into the midrange: Do you undergo an uncomfortable, invasive and likely unnecessary procedure? Or do you watch and wait (and worry) to see whether something more clearly worth investigating develops? The American Cancer Society projects that about 30,000 men will die of prostate cancer in 2005; it is the No. 2 cause of cancer death among U.S. men behind lung cancer. It generally appears after the age of 50, and in the U.S. is both more common and more deadly in black men than in whites or Asians.
"It is undisputed that PSA has an important role here, but we badly need additional tools," says Hans Lilja, a scientist at the Memorial Sloan-Kettering Cancer Center in New York who has worked on improvements to the PSA test and wasn't involved in the new study.
While the new approach holds the promise of providing clearer answers, outside experts -- and the researchers themselves -- caution that the method will require broader validation. This study relied on a small number of blood samples at two clinics. To be approved for widespread use by the Food and Drug Administration, the test would need to be backed by a substantially larger clinical trial.
Still, researchers and some other doctors say the results are compelling, and they may be applicable to other forms of cancer that also elicit antibodies. A small study published last year by researchers in Michigan showed, similarly, that certain antibodies appeared to be indicators of breast cancer. And the Michigan and Harvard researchers are studying applications to lung cancer as well.
The new testing method focuses not on the cancer itself or on any secretion from the prostate. Instead, it lets the body's own highly sensitive immune system make the determination. The test looks for particular antibodies -- or disease-fighting proteins -- that the immune system issues in response to cancerous tissues. "It's definitely a very novel approach," says David Shaffer, a medical oncologist at Memorial Sloan-Kettering, who wasn't involved in the study.
In the study of 257 blood samples, an intermediate PSA level -- between 2.5 and 10 billionths of a gram per milliliter -- was of little use as an indicator of prostate cancer, getting cancer status right only half the time. But for patients in that range, the antibody test nailed it 94% of the time. Overall the antibody test was 93% accurate in determining cancer status, versus 80% for the PSA test.
"I'm very confident that we can take advantage of the sensitivity of the immune system to detect cancer," says Arul Chinnaiyan, a urologist at the University of Michigan and one of the study's authors.
One potential caveat: The control group of blood samples was presumed cancer-free because its members have never had cancer and showed no signs of it. But no biopsies were performed among the controls, so that wasn't confirmed.
Understanding prostate cancer and determining courses of treatment can be vexing. The cancer is typically slow growing, and even patients with a positive biopsy face a difficult choice between doing nothing and watching the tumor's progression, and having surgery or radiation treatments that carry real risks of leaving them incontinent, impotent or both. The prostate gland, about the size of a walnut in adult men and adjacent to the bladder, secretes a fluid that becomes part of semen.
The PSA test, a simple blood screen that usually costs less than $50, has long stirred controversy among doctors who wonder whether patients are well served by identifying tumors that may be so slow-growing as to pose no threat, and also question its predictive value.
A broad study released last spring further confounded matters: It found prostate cancer in 15% of men with a PSA reading of four or less, a level generally considered normal by doctors.
Nevertheless, some doctors caution against abandoning the PSA test. "While it is a relatively dull knife with regard to being specific," says Durado Brooks, director of prostate- and colorectal-cancer programs for the American Cancer Society, "it remains the best, most widely available marker that we have for detecting prostate cancer."
Dr. Brooks notes that dozens of different prostate-cancer markers have been discovered in laboratories over the past several years, but none has yet proved accurate enough to replace PSA. Other methods for improving the accuracy of the PSA test itself have been studied, including measuring the rate of change in the level over time, taking sharp upswings as warning signs.
His advice for men 50 years old and older, or 45-year-olds with a risk factor such as race or family history: Monitor PSA levels and keep an eye out for changes. A PSA level of 3.9, bumping up against the bottom of the "normal" range, might be cause for testing more frequently than annually. Also, combine it with other tests such as a digital-rectal exam, in which a doctor examines the prostate with a finger via the rectum. A tactile exam can pick up abnormal growths that a PSA misses.
PSA tests are likely to remain critical in the evaluation of patients already diagnosed with cancer, in whom oncologists closely monitor shifts in PSA level to provide clues to how well a patient is responding to treatment, Dr. Shaffer says.
Write to Charles Forelle at
[email protected]
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