Stereotactic ablative RT may boost PFS

Stereotactic ablative radiotherapy (SABR) may help improve progression-free survival (PFS) and delay the need for systemic therapy in men with oligometastatic prostate cancer, according to a study presented at the Genitourinary Cancers Symposium in San Francisco.

Investigators conducted a study with 18 patients with relapsed oligometastatic prostate cancer and found that SABR may be beneficial and improve quality of life.

“Metastases-directed therapy (MDT) is one of the hottest topics in the management of advanced prostate cancer. The question is, can we do more to improve disease control, quality of life, and maybe cure some of the patients who relapse with few metastatic sites, up to three sites in this study,” said study investigator Ahmed El-Modir, MD, consultant oncologist at University Hospital Birmingham and Birmingham University, Birmingham, United Kingdom.

Dr. El-Modir and colleagues assessed both the efficacy and toxicity of SABR for oligometastatic recurrence. The oligometastatic state is considered an intermediate stage of cancer spread between localized disease and widespread metastases. The retrospective analyses looked at local control, biochemical progression-free survival (b-PFS), toxicity, and systemic therapy-free survival. Among the 18 patients, 26 lesions were treated with SABR, delivered using both CyberKnife and volumetric-modulated arc therapy.

In this cohort, clinicians used doses of 24 Gy in two or three fractions for spine and 30-40 Gy in three fractions for lymph nodes and other bony metastases. All patients were imaged prior to treatment and responses were determined by PSA testing and repeat scanning. The authors prospectively recorded acute and late toxicities using the Common Terminology Criteria for Adverse Events.

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“I was pleasantly surprised by how well tolerated and effective the treatment was. Trials with SABR for this indication are ongoing, but the results so far support the use of SABR in oligometastatic prostate cancer to improve progression-free survival and delay the need for systemic therapy,” Dr. El-Modir told Urology Times.

In the current study, the mean age of the men was 68 years and they all had previous treatments for the primary prostate cancer, including surgery (n=7), surgery and salvage prostate bed radiotherapy (n=6), radical radiotherapy (n=4), and cryotherapy (n=1). The cohort was heterogeneous, with 12 patients having a single metastatic site, four patients having two sites, and two patients having three sites. A short course of androgen deprivation therapy (ADT) was given in addition to SABR in six patients.

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The study showed that all the men experienced a decline in PSA levels, with a mean reduction of 75%. The median pre-SABR treatment PSA was 1.83 μg/L compared to a median post-SABR PSA of 0.28 μg/L. The investigators were pleased to find that 14 patients (78%) remained systemic therapy free at a median follow-up of 14 months (range, 2-28.5 months). When the authors looked at specific cases, they found three patients with a single pelvic lymph node metastasis achieved a sustained undetectable PSA level. In addition, all of the eight patients who had a post-treatment positron emission tomography scan showed no residual activity at the treated site. The adverse effects were tolerable and there were no toxicities above G1, except G2 acute bowel toxicity in one patient.

“Urologists should utilize PET scans to investigate rising PSA and detect early recurrence, which can be targeted with SABR. SABR is a promising treatment for oligometastatic prostate cancer. It is well tolerated with proven efficacy in a number of studies. Of course, it would be good to have data from phase III trials, but this a very heterogeneous group of patients and it would be very difficult to conduct such a trial. Patients also have a preference and sometimes opt for SABR rather than a trial,” Dr. El-Modir said.