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Many men with metastatic, hormone-sensitive prostate cancer live longer on continuous androgen-deprivation therapy (also known as hormone therapy) than on intermittent therapy, according to a 17-year study led by SWOG (formerly Southwest Oncology Group), a cancer research cooperative group.
The findings, based on the largest study ever of men with the disease, were presented June 3 at the American Society for Clinical Oncology's annual meeting in Chicago by the study's principal investigator, Dr. Maha Hussain of the University of Michigan Comprehensive Cancer Center. The Hutchinson Center's Dr. Cathy Tangen of the SWOG Statistical Center in the Public Health Sciences Division was one of the paper's co-authors.
Men with newly diagnosed metastatic prostate cancer are usually either surgically castrated or given medications to suppress the production of male hormones that drive their cancer. The treatment can help keep the disease at bay temporarily, but in the majority of patients the cancer will relapse and contribute to the patient's death.
Surgical castration is permanent but "medical castration" provides men the potential advantage of receiving therapy intermittently. A halt in this therapy is eventually followed by a rise in testosterone levels. Scientific data suggested that intermittent treatment may delay the cancer relapse, and that the rise in testosterone may result in an improvement in the patient's quality of life.
"Based on these results," Hussain said, "we can conclude that intermittent androgen-deprivation therapy is not as effective as continuous androgen-deprivation therapy in men with metastatic prostate cancer."
Clinical researchers from the SWOG network led an international team in conducting the study at more than 500 sites, enrolling 3,040 men with hormone-sensitive, metastatic prostate cancer between 1995 and 2008.
All men got an initial course of androgen-deprivation treatment for seven months. The 1,535 eligible men whose prostate-specific antigen (PSA) level dropped to 4 ng/mL or less by the end of those seven months were then assigned at random to stop therapy (the intermittent therapy group) or continue therapy (the continuous therapy group).
Those randomized to the intermittent therapy arm had their treatment suspended until their PSA rose to a predetermined level, at which time they started another seven-month course of androgen-deprivation therapy, cycling on and off therapy in this way as long as their PSA levels continued to respond appropriately during the "on" cycle.
Men on continuous therapy had a median overall survival time of 5.8 years from the time of randomization, with 29 percent of these men surviving at least 10 years. Those on intermittent therapy had a median overall survival time of 5.1 years, with 23 percent surviving at least 10 years from the time they were randomly assigned to a treatment arm.
The researchers found, in additional analyses, that men with "minimal disease" (disease that had not spread beyond the lymph nodes or the bones of the spine or pelvis) did significantly better on continuous therapy, while men with "extensive disease" (disease that had spread beyond the spine, pelvis, and lymph nodes or to the lungs or liver) seemed to do about as well using either treatment approach.
Additional analyses indicated that the median overall survival time for those with minimal disease was 7.1 years on continuous androgen-deprivation therapy compared to only 5.2 years on intermittent treatment. Patients with extensive disease had median overall survival times of 4.4 years on continuous therapy and 5.0 years on intermittent therapy.
'One size does not necessarily fit all'
"In the past when it came to using hormone therapy in this disease, doctors viewed the disease as one entity and adopted a 'one size fits all' approach," Hussain said. "Based on this study's findings, it seems that one size does not necessarily fit all."
Trial researchers also compared quality-of-life measures across the two study arms during the first 15 months following patient randomization, including measures of sexual function (impotence and libido), physical and emotional function, and energy level. They found improved sexual function in men who received intermittent therapy as compared to those on continuous therapy. A second presentation, led by the Hutchinson Center's Dr. Carol Moinpour (also of SWOG in PHS) at an ASCO poster discussion session on June 4 reported these preliminary quality-of-life findings.
SWOG is one of the five cooperative groups that together comprise the National Cancer Institute's National Clinical Trials Network. The group designs and conducts multidisciplinary clinical trials to improve the practice of medicine in preventing, detecting, and treating cancer, and to enhance the quality of life for cancer survivors. The Center houses SWOG's statistical center.
The National Cancer Institute and AstraZeneca Pharmaceuticals funded the study.
[Adapted from a SWOG news release]