Study offers combination treatment option for patients with oligometastatic prostate cancer

A new study offers a new option for patients with oligometastatic prostate cancer who want relief from hormone therapy without compromising the risk of spreading their disease. In the study, patients who received radiation therapy in addition to intermittent hormone therapy lived longer without their disease progressing, and they were able to take longer breaks from drug treatments. Results from the Phase II trial (EXTEND; NCT03599765) will be presented today at the annual meeting of the American Society for Radiation Oncology (ASTRO).

This study is the first randomized trial to assess the impact of adding radiotherapy to hormone therapy in patients with oligometastatic prostate cancer –; that is, those whose cancer has spread throughout the body to five or fewer lesions, or metastases.

Since most prostate cancer cells depend on testosterone to grow, standard treatment usually involves therapy to deprive the body of the hormone. A growing number of studies indicate that local therapies such as radiation therapy and surgery combined with hormone therapy can improve outcomes for patients with oligometastatic disease, and the EXTEND trial is the first to demonstrate this in a randomized clinical trial.

Using radiation therapy for oligometastatic prostate cancer can result in excellent tumor control and good long-term outcomes, and it may allow us to give these patients long breaks from hormone therapy.

Chad Tang, MD, study lead author and associate professor of radiation oncology, University of Texas at Houston MD Anderson Cancer Center

Hormone therapy is an effective tool for prolonging survival for patients with metastatic cancer, but it often causes harsh side effects, Dr. Tang said. Depletion of testosterone can lead to low energy, impotence and hot flashes – what might be referred to as “male menopause” – as well as an increased risk of cardiovascular disease, osteoporosis and of mental health disorders.

EXTEND is a collaborative trial involving adults with five or fewer metastases from different types of solid tumours. Dr. Tang’s team’s study is the leading prostate basket analysis, which recruited 87 participants who were on intermittent hormone therapy for prostate cancer. These patients were randomized to receive hormone therapy with (n=43) or without (n=44) local treatment. Local treatment options included radiation therapy, surgery, or cryotherapy to all sites of oligometastatic disease; all men in the trial received radiation therapy.

Patients received hormone therapy for at least two months before the start of the trial, and each participant stopped hormone therapy during a planned break six months after the start of the trial. Patients resumed hormone therapy when their disease progressed.

The researchers tracked the time until the patients showed evidence that their cancer had progressed, such as an increase in PSA. They also measured how long patients maintained normal testosterone levels after treatment before having to start hormone therapy again.

The median follow-up was 22.1 months and during this time the cancers of 41 patients progressed. Those who received local treatment in addition to hormone therapy experienced longer progression-free survival (median not reached versus 15.8 months for hormone therapy alone; HR 0.25, 95% confidence interval 0.12 -0.55, p

Fewer patients in the combination arm had new lesions two years after treatment (33% versus 41%, p=0.004). Patients in the combined group also had normal testosterone levels for longer than those who did not receive local treatment (p=0.03). Three serious (i.e. grade 3) side effects were observed in each treatment group.

The “powerful synergy” between radiation therapy and hormone therapy may be key to the promise of the combination treatment, Dr Tang said. “Hormone therapy has been shown in numerous studies to synergize with radiation therapy in reducing the ability of prostate cancer cells to repair themselves from radiation-induced DNA damage,” he explained. .

In addition to the clinical results, the research team also looked at the immune-stimulating effects of radiation. “In our study, we found increased T cell activation and other signals of greater immune activity in patients in the combination therapy group, but not in the hormone therapy alone group.”

After a patient’s prostate cancer metastasizes, the patient typically receives continued hormone deprivation. Dr. Tang said this study introduces a new paradigm of definitive radiation therapy for all of a patient’s oligometastases in tandem with defused intermittent hormone therapy as a way to preserve quality of life while maintaining disease control.


American Society of Radiation Oncology

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