In the SABR-COMET trial,1
random assignment was used to study the effects of ablative therapy in comparison to palliative radiotherapy. However, the authors noted that 30% of the control group received no palliative radiotherapy, whereas 24% of the stereotactic ablative radiotherapy (SABR) group received palliative radiotherapy in association with SABR—this execution was different from the proposed randomization. There was a significant difference in survival, with better survival in the group where all patients were treated with ablative therapy (42% vs. 18%). However, the authors noted that the primary endpoint was death from any cause, and cancer-specific mortality was not cited. This fact in addition to average age of participants being almost 70 years may represent a discrepancy in the analysis of the results.
It is also important to note the type of systemic therapy used in both groups was not specified. However, because the trial included tumors from multiple primary sites, it would have been difficult to assess the effect of therapy in distinct small groups. Additionally, because recruitment was completed in 2016, immunotherapy was not included in the groups studied. The question remains whether this type of therapy has been used more recently.
Primary lung cancer represented only 10% of enrolled patients. However, the lungs were sites of metastasis in almost half of the cases studied, and together with bone metastasis, constituted 80% of metastases. The authors reported that long-term survival was more prevalent for patients with breast, prostate, and kidney cancers, suggesting that the study has little or no value for patients with primary lung cancer. Even considering the reported data, the statistical significance of this phase II study was marginal to consider the evidence as definitive (p = 0.006).
In summary, local control of oligometastic disease using ablative therapy is promising; however, despite the study being randomized, it is difficult to establish that the best survival in the treatment group was most related to the use of SABR.
- 1. Palma DA, Olson R, Harrow, S, et al. Stereotactic Ablative Radiotherapy for the Comprehensive Treatment of Oligometastatic Cancers: Long-Term Results of the SABR-COMET Phase II Randomized Trial. J Clin Oncol. 2020;38(25):2830-2838.