Oct. 8 (HealthDay News) -- For several years, doctors have debated the value of the prostate-specific antigen test to determine a man's risk for prostate cancer.

But now, a consensus seems to be emerging -- it's not the level of the antigen in the blood that helps predict the likelihood of aggressive disease, but whether that level is rising rapidly or not.

Men with prostate-specific antigen (PSA) levels that are growing rapidly -- even if those levels are still low -- should consider themselves at increased risk, said Howard Soules, executive vice president for the Prostate Cancer Foundation, the world's largest philanthropic source of support for prostate cancer research.

"Right now, if your PSA velocity is going up at an extreme rate, you need some additional monitoring for prostate cancer," Soules said.

The prostate gland, which produces seminal fluid, is part of the male reproductive system and is located in front of the rectum and under the bladder. It surrounds the urethra, the tube through which urine flows, and when healthy is about the size of a walnut.

Prostate cancer is the second most common type of cancer among men in the United States and the second leading cause of cancer death, according to the American Cancer Society. Only skin cancer is more common, and only lung cancer kills more men.

The cancer society estimates there will be about 218,890 new cases of prostate cancer in the United States in 2007, and about 27,050 men will die of the disease. Of every three men diagnosed with cancer each year, one is diagnosed with prostate cancer.

Despite its prevalence, prostate cancer is quite survivable. Overall, 99 percent of men diagnosed with prostate cancer live at least five years, according to the cancer society. And 92 percent survive at least a decade, and 61 percent at least 15 years. While one in six men will get prostate cancer during his lifetime, only one in 34 will die of the disease.

"We're seeing people living 15 to 20 years with their prostate cancer, which we didn't see in the '80s and '90s," said Dr. Susan Slovin, chairwoman of the National Prostate Cancer Coalition's scientific advisory board.

But the key is early detection.

Ninety percent of all prostate cancers are found still within the prostate gland, or only in nearby areas, according to the American Cancer Society. For those patients, the five-year survival rate is nearly 100 percent. But for the men whose cancer has spread to distant parts of the body when it is diagnosed, the five-year survival rate falls to 34 percent.

The cancer society recommends annual screenings for prostate cancer beginning at age 50 for most men, and at age 45 for men at high risk. Those at high risk include blacks and men who've had a close relative suffer from prostate cancer before age 65.

The screening involves two steps: undergoing a digital rectal exam and testing for PSA levels in the blood.

In the rectal exam, the doctor feels the prostate to see if there are any bumps or hard spots that might signify cancer.

And although PSA is not an indicator of cancer, but a protein created during inflammation of the prostate, doctors have found that highly elevated levels indicate an increased risk for cancer.

Studies now show that the regular testing of PSA levels can indicate cancer risk by showing rises or falls in the protein's levels.

"They've been trying to see if you can use PSA as a predictor by looking at a trend," Soules said. "It's met with some good success."

PSA trends -- or PSA "velocity," as doctors refer to it -- also can help guide treatment for prostate cancer, said Slovin, an assistant member of the Genitourinary Oncology Service at Memorial Sloan-Kettering Cancer Center, and an assistant professor at New York Hospital-Weill Medical College, both in New York City.

"If we see a treatment is bringing the PSA down rapidly, that's obviously a response," she said. "But if it's not changing, or increasing, we should consider switching treatments."

If prostate cancer is suspected, the patient must undergo a biopsy to determine if it is present.

An alternative to biopsy is showing much promise, Slovin noted.

Using an MRI screening of the patient in tandem with an endorectal probe -- a rubber, gel-filled "finger" that presses against the rectal wall -- doctors are getting astonishing results, she said.

"You can get an almost textbook picture of what's on the other side of the rectal wall," she said. "It shows if cancer has spread, and how invaded the prostate is. It's also minimally invasive compared with biopsies."

SOURCES: Howard Soules, Ph.D., executive vice president, the Prostate Cancer Foundation, Santa Monica, Calif.; Susan Slovin, M.D., Ph.D., chairwoman of the Scientific Advisory Board for the National Prostate Cancer Coalition, an assistant member of the Genitourinary Oncology Service at Memorial Sloan-Kettering Cancer Center, and an assistant professor at New York Hospital-Weill Medical College, New York City; American Cancer Society; National Cancer Institute