Stereotactic Ablative Radiotherapy for the Comprehensive Treatment of Oligometastatic Cancers: Long-Term Results of the SABR-COMET Phase II Randomized Trial
- Study type
- Clinical trial
- Study name
- SABR-COMET
- Phase
- Phase 2
- Design
- Randomised phase 2 trial with a screening design, international multicentre, with 1:2 randomisation
- Sample size
- 99 patients (10 centres)
- Source
- JCO · 2020
In plain words
In this study, patients whose cancer had spread to a small number of spots in the body (1 to 5) either received only the usual palliative treatments or, in addition, received very precise, high-dose radiotherapy called SABR to all of these spots. After 5 years, about 42% of patients in the SABR group were alive, compared with about 18% in the usual-treatment group. No new side effects were seen and quality of life did not differ between the two groups. Whether this approach suits a particular patient should be decided by the treating doctor and the radiation oncologist.
Key results
Treatment arms and regimens
Standard palliative care: conventional palliative radiotherapy aimed at symptom relief or prevention of complications, with recommended doses from 8 Gy in 1 fraction to 30 Gy in 10 fractions; standard palliative systemic therapy when indicated, at the oncologist's discretion (pragmatic approach) (33 patients).
Standard of care plus stereotactic ablative radiotherapy (SABR) to all metastatic lesions (1 to 5 lesions); dose and number of fractions according to lesion site from the protocol table of permitted doses (data supplement), respecting organ-at-risk dose constraints, with peer review of all treatment plans. If new metastases developed, repeat SABR was allowed where feasible. Palliative systemic therapy as in arm 1 (66 patients). The SABR dose table was not reviewed in this session.
Source of the regimen details: Full text of the JCO 2020 paper (PMC7460150, Procedures section); the table of permitted SABR doses is only in the appended protocol and was not verified here
Doses are given for the information of specialists, as in this study’s protocol, and are not a prescription. Every drug must be prescribed by the treating physician for the individual patient.
Study population
Adults (≥18 years) with ECOG 0 or 1, life expectancy ≥6 months, a controlled primary tumour and 1 to 5 metastases, all suitable for SABR within the protocol dose constraints. Exclusion criteria: serious comorbidity precluding radiotherapy, prior radiotherapy to a site requiring treatment, malignant pleural effusion, tumour within 3 mm of the spinal cord and brain metastasis requiring decompressive surgery. Stratified by number of metastases (1 to 3 versus 4 to 5). Most common primary tumours: breast (18), lung (18), colorectal (18) and prostate (16).
Endpoints
Primary endpoint: overall survival (OS), using an alpha of 0.20 (P below 0.20 meaning a positive trial). Secondary endpoints: progression-free survival (PFS), toxicity and quality of life (QOL).
Safety and side effects
No new grade 2 to 5 adverse events were reported with long-term follow-up; the overall rate of grade ≥2 treatment-related adverse events therefore remained 9% (3 of 33) in the control arm versus 29% (19 of 66) in the SABR arm (P = 0.03; absolute increase 20%). The rate of treatment-related death (grade 5) in the SABR arm was 4.5%, despite strict dose constraints and review of all plans. No difference in quality of life was seen between the two arms.
Clinical significance and place in guidelines
This randomised phase 2 trial showed that adding SABR to standard of care in oligometastatic patients was associated with improved overall survival and progression-free survival, and the effect was sustained with long-term follow-up. However, the study used a phase 2 screening design with an alpha of 0.20 and a limited number of patients, so the results need confirmation in phase 3 trials. Its place in clinical guidelines should be checked separately.
Limitations
The phase 2 screening design with an alpha of 0.20 (a more liberal threshold than usual), the relatively small sample size (99 patients) and the heterogeneity of primary tumour types are limitations of the study. The number of patients with each tumour type is insufficient for tumour-specific conclusions. Dose details and other limitations should be checked in the full text.
This summary was prepared by the editorial team from the published paper; the original paper is the final reference. Read the original abstract on PubMed.