MUNICH – Radiotherapy of the primary tumor can improve overall survival in men with untreated metastatic adenocarcinoma of the prostate, a finding that suggests a possible life-extending role of radiotherapy in other metastatic tumor types, investigators in thetrial reported.
Among 2,061 men from the United Kingdom and Switzerland with previously untreated metastatic prostate cancer, there was no survival advantage to adding local radiation to standard drug therapy in the overall study population. But among men with low disease burden (local invasion of bone or lymphatics) radiation to the prostate plus standard of care was associated with a 32% improvement in overall survival compared with standard therapy alone, said Chris Parker, MD, from the Royal Marsden NHS Foundation Trust.
“Prostate radiotherapy is a simple treatment, it’s very well tolerated, and it’s widely available in any cancer center throughout the world,” Dr. Parker said in a briefing prior to his presentation in a presidential symposium at the European Society for Medical Oncology Congress.
The study was published online into coincide with the presentation.
Men who first present with metastatic prostate cancer account for about 10% of prostate cancer patients in the Western world, but may comprise as much as 60% of the prostate cancer population in some parts of Asia, noted briefing moderator and discussant, from the Hospital Universitario Marques de Valdecilla, in Santander, Spain.
Prior to, “we had never considered treating the local tumor in the context of wider-spread disease, and this is what the group of STAMPEDE really answered today with this study,” he said. “I think there is a substantial group of prostate cancer patients who might benefit from that. This opens the door to apply a new treatment that may have an impact in the life of these patients.”
The overarching goal of the STAMPEDE (Systemic Therapy in Advancing or Metastatic Prostate Cancer: Evaluation of Drug Efficacy) study is to assess novel approaches for men with hormone-naive prostate cancer.
For this aspect of the randomized, phase 3 trial, 2,061 men with newly diagnosed M1 prostate cancer were enrolled and randomly assigned to either androgen deprivation with or without docetaxel or to the same standard of care plus radiotherapy. Radiation was delivered in one of two schedules: 55 Gy delivered in 20 fractions over 4 weeks or 36 Gy in 6 fractions delivered over 6 weeks, started within 8 weeks of randomization or the start of docetaxel.
As noted before, death from any cause, the primary endpoint, was not significantly different between the study arms. But in a subgroup analysis by metastatic burden, the rate of 3-year overall survival in patients with low burden was 81% in the radiotherapy group, compared with 73% in the standard-of-care arm. The hazard ratio was 0.68 (P = .007) favoring radiation.
In contrast, the 3-year overall survival rate in the high metastatic burden arm (patients with four or more metastases to bone with at least one outside the axial skeleton and/or visceral metastases) was 53% with radiation, versus 54% without.
In all, 5% of patients in the radiotherapy arm had grade 3 or 4 adverse events during therapy, and 4% had postradiation adverse events.
Radiation was associated with small increases in the risk for bladder and bowel events, but these were generally “modest” in nature and were outweighed by the survival benefit, Dr. Parker said.
He noted that men with regional nodal invasion but not metastases were not included in the trial. “However, if prostate radiotherapy improves survival for men with distant metastases, we can be very confident that it would improve survival for men with regional nodal disease. There aren’t any trials addressing that question, and currently many of these men receive drug treatment alone. So going forward, prostate radiotherapy should be the standard treatment for these men as well.”
The concept of primary tumor irradiation may work for patients with other malignancies who have low burden (oligometastatic) disease, he added.
“Based on the findings of STAMPEDE, radiotherapy could be considered for patients with newly diagnosed oligometastatic prostate cancer, but further studies are needed to delineate the clinical implementation of such treatment,” commented, from the Mayo Clinic in Rochester, Minnesota, and his colleagues, in an accompanying the article in the Lancet Oncology.
The study is sponsored by the Medical Research Council of the United Kingdom. Dr. Parker disclosed research funding and personal fees from Bayer and personal fees from Advanced Accelerator Applications and Janssen Pharmaceuticals. Dr. Duran disclosed participation in compensated advisory boards for Roche and Bristol-Myers Squibb and speaker honoraria from Roche, Bristol-Myers Squibb, and Merck.
SOURCE: Parker C et al. ESMO 2018, .