Doctors have suspected that radiation therapy helped prevent patients from dying of prostate cancer, but had little scientific proof. Now, Richard Valicenti, M.D., assistant professor of radiation oncology at Jefferson Medical College of Thomas Jefferson University in Philadelphia, and his colleagues have found the first conclusive evidence that radiation therapy helps patients with localized prostate cancer live longer.
He presents his team's findings May 16 at the annual meeting of the American Society of Clinical Oncology in Atlanta.
Prostate cancer, the most common cancer in elderly men, tends to be a slow growing disease men frequently die with, not from. Doctors often question whether surgery or radiation provide any real benefit for the older patient.
The researchers retrospectively examined the results of 1560 patients who had received radiation therapy alone for prostate cancer. The patients were among those treated between 1975 and 1995 in four separate trials conducted by the Radiation Therapy Oncology Group, a federally funded cancer clinical trials group. The average follow up was eight years, with some patients seen for as many as 12 years.
They found that in dividing men into four categories according to the likelihood of having a more dangerous cancer, those with the worst prognoses benefited the most from receiving higher doses of radiation. After they adjusted statistically for disease severity and age, they found that patients who received higher-than-usual radiation doses were 32 percent less likely to die from prostate cancer.
"I think these results will change how we evaluate the use of higher radiation doses and new radiation treatment systems for prostate cancer," Dr. Valicenti says.
Dr. Valicenti's group wanted to try to answer the question, "Is there an advantage to treating prostate cancer locally with radiation therapy?" To accomplish this, they evaluated patients according to their risk of dying from the disease.
Dr. Valicenti, a member of Jefferson's Kimmel Cancer Center, and his co-workers at Jefferson, Wayne State University in Detroit, the University of Southern California, McAuley Health Center in Ann Arbor, MI, and Einstein Medical Center in Philadelphia examined patients' Gleason scores. The Gleason score is a way of grading the pathology of a cancer cell. Undifferentiated or poorly differentiated cells are more abnormal and characteristic of more aggressive cancers. The higher the Gleason score, the poorer the patient's prognosis.
They evaluated these scores and the varying radiation doses patients in four separate studies had received. They found that overall, patients with the highest Gleason scores (between 8 and 10, on a scale of 2 to 10) who should have had the worst prognoses and who received a higher radiation dose, had better local control of their cancer, and were more likely to be disease-free and alive longer.
"Radiation therapy provides an overall survival benefit for clinically localized prostate cancer for those with a Gleason score between 8 and 10," Dr. Valicenti says. "Those less than 8 didn't experience an observable advantage with followup to 12 years.
"We were happy to see improvement of local control with higher radiation doses," he says. "This would suggest in part that the disease-free survival advantage is attributed to improved tumor control."
The work was funded in part by the National Cancer Institute.
The prostate is a walnut-sized, male sex gland located below the bladder and directly in front of the rectum. During intercourse, it produces a thick fluid that helps force sperm through the urethra and out of the penis.
Since 1990, the reported new cases of prostate cancer have more than tripled, from less than 100,000 annually to more than 300,000, owing to better detection and greater public awareness. More than 60,000 men a year receive radiation therapy for localized disease. More than 40,000 men will die from prostate cancer this year, making it the second leading cause of cancer death among men in the United States.