SBRT and Hormone Therapy May Delay Advanced Prostate Cancer Progression

“These initial results could be fantastic news for advanced prostate cancer patients,” said Dr. Alison Tree, discussing findings on SBRT and hormone therapy in advanced prostate cancer.

Administration of radiotherapy in conjunction with hormone treatment has been shown to potentially delay disease progression among some patients with advanced prostate cancer, researchers have found.

Findings from the phase 2 TRAP trial conducted by researchers from United Kingdom’s Royal Marsden NHS Foundation Trust and the Institute of Cancer Research in London, purported to be the first trial investigating the use of stereotactic body radiotherapy (SBRT) among patients with hormone-resistant oligoprogressive [when tumor cells form new tumors or lesions in fewer than three sites] prostate cancer, were presented at the European Society for Radiotherapy and Oncology (ESTRO) annual congress.

Researchers on the TRAP study recruited 86 patients with castration-resistant prostate cancer with two or fewer sites of oligoprogressive disease (OPD) that had developed during treatment with an androgen receptor targeted agent therapy.

Eighty-one patients, with a mean age of 74, received SBRT, according to study findings posted to the ESTRO website. The majority of patients, 67%, had one OPD lesion, while 58% of patients were receiving treatment with the Zytiga (abiraterone) and 42% were being treated with Xtandi (enzalutamide).

Researchers found a 40.1% 12-month progression-free survival (PFS; the time a patient lives without their disease spreading or progressing) rate, as well as a median post-SBRT PFS time of 6.4 months.

SBRT, according to the National Cancer Institute, precisely delivers radiation to tumors in the patient’s body, with doses of radiation given over several days, with the intention of sparing healthy tissue.

At a median follow-up time of 19.2 months, 53 (65%) of patients had progressed, with 32 (40%) of patients having progressed within six months of receiving SBRT. The median time to next treatment was 29.6 months, the median overall survival (the time a patient lives following treatment, regardless of disease status) time was 34.6 months and 33 (41%) of patients had started new treatment or died, researchers reported.

Of the 43 patients with evaluable levels of prostate-specific antigen (PSA; a protein associated with the presence of prostate cancer in the body) who had not progressed or died within six months of receiving SBRT, 84% had experienced reductions of PSA greater than 75% at six months after SBRT, researchers found. This was compared with 45% of patients who had progressed or died within six months.

Researchers reported that four patients died within six months after SBRT for reasons unrelated to radiotherapy treatment, and that severe or higher side effects and toxicity were reported in seven patients, “with up to two events potentially associated with SBRT.”

“These initial results could be fantastic news for advanced prostate cancer patients,” said Dr. Alison Tree, in a news release issued by The Institute of Cancer Research. Tree is a consultant clinical oncologist at the Royal Marsden NHS Foundation Trust, Honorary Reader at The Institute of Cancer Research and Chief Investigator of the TRAP trial.

“We are focused on developing smarter, kinder and better treatments for patients across the UK and internationally,” said Tree. “Currently, treatment options for men with advanced prostate cancer are limited, however I hope that after we have conducted larger studies to confirm our findings, we will see this change and we will be able to treat these patients very differently, using radiotherapy as standard to target drug-resistant parts of the cancer. Radiotherapy is well-tolerated and significant side effects are rare, so we hope this treatment will in the future delay the need for chemotherapy, protecting quality of life for longer.”

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