Adding prophylactic radiotherapy to standard care appears safe and effective for treating asymptomatic bone metastases in patients with solid tumors, according to a phase 2 trial presented at the 2022 ASTRO Annual Meeting.

Prophylactic radiotherapy reduced skeletal-related events (SREs) and improved overall survival (OS) when added to standard care, said study presenter Erin Gillespie, MD, of Memorial Sloan Kettering Cancer Center in New York, New York. 

Dr Gillespie and colleagues tested prophylactic radiotherapy in a phase 2 trial (ClinicalTrials.gov Identifier: NCT03523351) of 78 patients with asymptomatic bone metastases. The patients were randomly assigned to receive prophylactic radiotherapy plus standard care (n=39) or standard care alone (n=39). 


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The median age was 65 years in the standard care-alone arm and 61 years in the radiotherapy arm. The most common cancers were lung (26% in the standard arm and 28% in the radiotherapy arm), breast (23% and 26%, respectively), and prostate (23% and 21%, respectively). 

In both arms, the planned standard care was systemic therapy for 90% of patients and surveillance for 10%. About half of patients in each arm received a bone-modifying agent. 

For patients in the radiotherapy arm, clinicians could choose the dose based on prespecified options. The radiotherapy dose was 27 Gy in 3 fractions for 31% of patients, 20 Gy in 5 fractions for 24%, 8 Gy in 1 fraction for 15%, and 30 Gy in 10 fractions for 13%.

The primary endpoint was SREs, which were defined as pathologic fracture, cord compression, surgery for instability, or radiotherapy for pain. The rate of SREs was significantly lower with prophylactic radiotherapy than with standard care alone — 1.6% and 29%, respectively (P <.001). 

Hospitalization for SREs was also significantly lower with prophylactic radiotherapy. There were no hospitalizations in the radiotherapy arm and 4 hospitalizations in the standard care arm (P =.045). Pain was significantly lower at 12 months in the radiotherapy arm than in the standard care arm as well (P =.039). 

At a median follow-up of 2.41 years, the median OS was 1.67 years with radiotherapy and 0.99 years with standard care alone (hazard ratio [HR], 0.49; 95% CI, 0.27-0.89; P =.018). In a multivariate analysis, receipt of radiotherapy was significantly associated with improved OS (HR, 0.45; 95% CI, 0.24-0.84; P =.011). 

The rate of grade 2 treatment-related adverse events (TRAEs) was 13% with radiotherapy and 3% with standard care alone. The most common grade 2 TRAEs in the radiotherapy arm were fatigue (10%) and nausea (8%). There were no grade 3 TRAEs in the radiotherapy arm.

These data suggest a “promising new indication for radiation,” Dr Gillespie said. She added that more work is needed to optimize use and identify patients who could benefit from prophylactic radiotherapy.

Disclosures: Some study authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of disclosures.

Reference

Gillespie EF, Mathis NJ, Marine C, et al. Prophylactic radiation therapy vs. standard-of-care for patients with high-risk, asymptomatic bone metastases: A multicenter, randomized phase II trial. ASTRO 2022. October 23-26, 2022. Abstract LBA04.