medwireNews: Stereotactic ablative radiotherapy (SABR) is associated with “clinically acceptable” rates of toxicity, local control, progression-free survival (PFS), and overall survival (OS) in people with oligometastatic cancer, meta-analysis data suggest.
However, Nicholas Zaorsky (Penn State Cancer Institute, Hershey, Pennsylvania, USA) and colleagues say that their findings “are not meant to be viewed as definitive evidence that SABR is safe and effective in all patients with oligometastatic cancer,” but instead are “intended to be hypothesis generating as we await the results of further prospective trials.”
The analysis included data from 21 single- or multi-arm prospective trials among 943 patients (median age 63.8 years) with oligometastatic cancer (≤5 sites of extracranial disease), who received a maximum of eight SABR fractions at a dose of at least 5 Gy/fraction. The studies were published between 2004 and 2020.
The most common primary tumor sites were the prostate (22.9%), colorectum (16.6%), breast (13.1%), and lung (12.8%), while the most frequently treated lesions by SABR were in the bone and/or spine (44.8%), lung (29.2%), liver (13.1%), and lymph nodes (12.2%).
Zaorsky and co-authors report in JAMA Oncology that 12 trials documented the rate of acute grade 3 to 5 toxic effects, which ranged from 0.0% to 20.0%. The pooled random-effects analysis found that the overall estimate was 1.2%.
For late grade 3 to 5 toxic effects, the pooled rate was 1.7% with a range of 0.0% to 10.0% across 12 trials.
Zaorsky and team also reviewed 1-year local control, OS, and PFS rates. The random-effects estimates for these were 94.7% (range 67.2–100%), 85.4% (65.9–100%), and 51.4% (33.3–80.0%), respectively.
The researchers say their findings “provide evidence in support of SABR across a variety of primary tumor histologic characteristics given its excellent [local control] and perhaps more importantly low overall rates of severe acute and late toxic effects, which is particularly important in the context of patients with metastatic disease and limited life expectancies.”
But they caution that “the low rates of toxic effects are likely to be a result of well-selected patients,” and also note that there was a significant amount of heterogeneity among the trials.
The authors suggest: “This large amount of heterogeneity was likely present because the prospective data presently available were not limited to a single tumor histologic type, the studies had varying inclusion and exclusion criteria, and the studies primarily involved treatment to different sites.”
They conclude: “Future prospective studies should aim to further stratify these factors to better elucidate sources of heterogeneity, which would allow for SABR to be tailored in a more individualized manner.”
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