SABR may improve survival in oligometastatic cancer
medwireNews: The phase II SABR-COMET study has indicated that stereotactic ablative radiotherapy (SABR) prolongs overall and progression-free survival versus palliative treatment in patients with up to five oligometastases.
Patients with a controlled primary tumor and one to five oligometastases were enrolled into the study, with 66 allocated to receive SABR and 33 to receive palliative care. Median overall survival was 13 months longer in those who underwent SABR, at 28 versus 41 months, giving a hazard ratio, albeit nonsignificant, of 0.57.
In all, 36% of patients in the SABR group died from any cause over a median follow-up of 26 months, compared with 48% of patients over a median follow-up of 25 months in the palliative care group.
Progression-free survival was doubled with SABR versus palliative care, at 12 and 6 months, respectively, giving a significant hazard ratio of 0.47.
The hypothesis of oligometastases suggests a state of tumor progression between purely localized and widely metastatic disease. To date, however, evidence supporting the potential for improved outcomes in those with oligometastases has generally been limited to nonrandomized, observational studies.
The current findings “represent the strongest level of evidence, thus far, in support of the existence of an oligometastatic state,” write researcher David Palma (London Health Sciences Centre, Ontario, Canada) and colleagues in The Lancet.
Although the overall survival result met the prespecified endpoint for this phase II trial, the researchers note that they included patients with multiple cancer types and so “phase 3 trials in single disease cohorts might be required to provide definitive evidence of an overall survival benefit in a broader spectrum of patients presenting with oligometastases.”
They add that such trials, including studies specific to lung and breast cancer, are ongoing. However, the significance of the progression-free survival benefit (p=0.0012) could, in the absence of phase III data, be considered “a definitive result,” says the team.
However, the survival improvements came at the cost of increased toxicity. Although SABR was well tolerated by the majority of patients, three (4.5%) patients in the SABR group died as a result of toxicity despite “stringent” dose constraints. The researchers therefore suggest that “SABR delivery should continue to focus on minimisation of toxicity and that the use of SABR in patients with more than five lesions should be done in the context of a clinical trial.”
Indeed, only a small number of patients in the trial (five in the SABR group and two in the control arm) had four or five metastases, limiting the conclusions that the researchers could make about such patients. This highlights the need for randomized trials to “define the maximum number of metastases wherein SABR still provides a benefit,” they say.
Commenting on the study in a related article, Billy Loo Jr and Maximilian Diehn, both from Stanford University School of Medicine, California, USA, said that the results of this study, combined with previous findings, “collectively provide the highest level of evidence to date for definitive local therapy in the management of metastatic cancer.”
By Catherine Booth
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