Background
Phase II RCT (SABR-COMET). 99 patients with controlled primary tumor and 1–5 oligometastases across various histologies (lung, breast, prostate, colorectal, and others). Randomized 1:2 to palliative standard-of-care (SoC) alone vs SoC + SABR/SBRT to all metastatic lesions. First randomized trial to test SABR for oligometastatic disease across tumor types.
Interventions and follow up
Arm A: Palliative SoC alone (systemic therapy, supportive care per physician discretion) — 33 patient
Arm B: SoC + SABR to all oligometastatic lesions (dose/fractionation per site: lung 54 Gy/3; bone 20–35 Gy; liver/adrenal 45–60 Gy/3) — 66 patient
Primary endpoint: OS
mFollow up: 5.1 years (median)
Arm B: SoC + SABR to all oligometastatic lesions (dose/fractionation per site: lung 54 Gy/3; bone 20–35 Gy; liver/adrenal 45–60 Gy/3) — 66 patient
Primary endpoint: OS
mFollow up: 5.1 years (median)
Results
5-yr OS (SABR): 42.3% vs SoC 17.7%, HR 0.57, P=.09
mOS (SABR): 50 months vs SoC 28 months
PFS: 12 months (SABR) vs 6 months (SoC), HR 0.47, P=.001
Response rate to SABR: Local control of treated lesions 79% at 6 months
mOS (SABR): 50 months vs SoC 28 months
PFS: 12 months (SABR) vs 6 months (SoC), HR 0.47, P=.001
Response rate to SABR: Local control of treated lesions 79% at 6 months
Adverse events
Main adverse events: Grade ≥2 toxicity: 29% (SABR) vs 9% (SoC). Grade ≥3: 3 patients in SABR arm with serious adverse events (rib fracture, radiation pneumonitis, GI perforation). Treatment-related deaths: 1 (SABR — grade 5 GI perforation after liver SABR). No grade ≥3 in SoC arm.
Conclusions
SABR was associated with a clinically meaningful but non-statistically-significant improvement in OS (HR 0.57) in this underpowered phase II trial. PFS was significantly improved. The results supported proceeding to confirmatory phase III (SABR-COMET-3, SABR-COMET-10) but cannot be considered definitive evidence of OS benefit.
Key Limitations
Key Limitations: Underpowered phase II trial (99 patients) — OS result does not meet statistical significance. Heterogeneous tumor types limit interpretation for specific cancers. SoC arm was not standardized. One treatment-related death in SABR arm. Selection bias favors favorable-prognosis patients; results cannot be generalized to all oligometastatic patients.
Clinical Context
SABR-COMET is the most cited evidence for SABR in oligometastatic disease despite its phase II status and non-significant OS result. Confirmatory phase III SABR-COMET-3 (3 metastases) and SABR-COMET-10 (4–10 metastases) are ongoing. Most oncology guidelines recommend multidisciplinary discussion for SABR in oligometastatic disease but do not yet mandate it as standard of care.
References