SBRT favorable for extracranial oligometastases
medwireNews: Patients with extracranial oligometastases derive a long-term survival benefit from stereotactic body radiotherapy (SBRT), research suggests.
Factors mediating a good survival outcome include the location of the primary tumor and metastases, plus the length of time between initial diagnosis and oligometastasis presentation, report the investigators.
The study involved 1033 patients with 1–5 extracranial oligometastases whose primary tumor was treated with curative intent. Over half of the study participants (57.7%) had one oligometastasis, 23.7% had two, 10.2% had three, 5.3% had four, and 3.1% had five. For the majority (89.9%) of patients, the metastases were in a single organ, most commonly the lung (44.6%), bone (29.8%), or liver (13.3%).
Over a median 24.1-month follow-up, the median overall survival (OS) for the cohort was 44.2 months, with 1-, 2-, 3-, and 5-year OS rates of 84.1%, 69.6%, 56.7%, and 35.2%, respectively.
However, the researchers say that the progression-free survival (PFS) duration was “modest,” at a median of 12.9 months. And they point out that with 1- and 2-year PFS rates of 52.1% and 30.8%, respectively, “most of the population with oligometastases in the present study continued to relapse within a short time frame.”
To further elucidate the pattern of disease progression after SBRT, the researchers used a “novel metric” of widespread progression (WSP), which they defined as the time to further metastatic dissemination.
The median time to WSP was 42.5 months, which the team says “suggests that WSP is not an early pattern of progression.” However, they note that 31.2% of patients who progressed had WSP, over a short median time of 5.7 months.
“This result highlights the ongoing challenge of defining the optimal patient cohort that can benefit from upfront SBRT vs systemic therapy,” note Ian Poon (University of Toronto, Ontario, Canada) and colleagues.
They carried out multivariable analyses finding various “[f]actors that can inform clinical decision-making and clinical trial design,” including the time to and site of oligometastasis presentation, and primary tumor type.
Patients were a significant 51% less likely to die if their metastases were confined to the nodes or soft-tissue, and 42% less likely if they were confined to the lungs, versus other locations. The researchers say that due to the small sample size (n=51) of patients with nodal or soft-tissue metastases, these results need to be validated, whereas the large sample size (n=414) of patients with lung metastases “likely resulted in the significance observed.”
The risk for death was also significantly reduced by 37% among patients who developed an oligometastasis at least 24 months after their primary tumor diagnosis versus within 24 months.
Primary tumor type was an important factor associated with survival outcomes, the researchers note. Patients with a primary tumor in the prostate had the longest OS with the median not reached during the study period, followed by patients with tumors in the kidney at a median OS of 82 months, the breast at 51 months, the colon or rectum at 49 months, and the lung at 32 months, respectively.
The researchers say SBRT had a “favorable” safety profile, noting that there were 66 grade 3 or higher adverse events (AEs). The most common acute AEs (n=31) were pain, fatigue, and pneumonitis, and the most common late AEs (n=35) were pneumonitis, pain, and cough. One patient with bile duct stenosis died, which the study authors attributed to SBRT.
Poon and colleagues conclude in JAMA Network Open: “Phase 3 [randomized controlled trials] are needed to confirm the OS and PFS benefits of extracranial [oligometastases] ablated with SBRT. However, the data in this study provide a benchmark of [oligometastases] outcomes and identify meaningful factors associated with OS.”
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