SABR benefits men with oligometastatic prostate cancer
medwireNews: Stereotactic ablative radiotherapy (SABR) is associated with a significantly lower risk for disease progression at 6 months relative to observation in men with oligometastatic prostate cancer, phase 2 study data show.
Phuoc Tran (Johns Hopkins University School of Medicine, Baltimore, Maryland, USA) and co-investigators say their findings “are consistent with prior reports validating the existence of the oligometastatic state in prostate cancer and the utility of SABR as MDT [metastasis-directed therapy] in this condition.”
The ORIOLE trial included 54 men (median age 68 years) with recurrent hormone-sensitive prostate cancer and 1–3 asymptomatic metastases detectable by conventional imaging. The men may have previously received up to 3 years of androgen deprivation therapy (ADT) but not within 6 months of enrollment.
At 6 months from baseline, 19% of the 36 patients randomly assigned to receive SABR (19.5–48.0 Gy in 3–5 fractions) had disease progression, defined as a prostate-specific antigen level increase of at least 2 ng/dL, progression on conventional imaging, symptomatic progression, initiation of ADT, or death.
By comparison, disease progression occurred in 61% of the 18 patients randomly assigned to undergo observation only.
Median progression-free survival (PFS) was not reached among the patients who received SABR and was 5.8 months among those who underwent observation, resulting in a significant hazard ratio (HR) for disease progression or death of 0.30 in favor of SABR.
The researchers note in JAMA Oncology that 44% of patients treated with SABR had baseline positron emission tomography (PET)-avid lesions that were not included in the treatment fields because the researchers were blinded to prostate-specific membrane antigen (PSMA)-targeted PET data during treatment planning.
Of these, 38% had disease progression at 6 months, compared with 5% of the men who had all lesions treated with SABR. Median PFS in these two groups was 11.8 months and unreached, respectively, corresponding to a significant HR for disease progression or death of 0.26 in favor of SABR.
The men in the SABR group with untreated lesions were also significantly more likely to develop new metastatic lesions at 180 days than those with no untreated lesions (62.5 versus 15.8%) and have a significantly shorter median distant metastasis-free survival (6.0 vs 29.0 months).
Tran et al say: “These data support the use of molecular imaging in conjunction with MDT for patients with [oligometastatic prostate cancer].”
The investigators also found that baseline immune phenotype and a tumor mutation signature may be associated with clinical response to SABR, but say this hypothesis requires validation in independent cohorts.
Tran et al conclude: “Although SABR alone may or may not be sufficient as curative management [of oligometastatic prostate cancer], the combination of SABR with systemic therapies may provide the multipronged attack required to cure this disease.”
In an accompanying comment, Carlo Greco and Zvi Fuks, both from the Champalimaud Centre for the Unknown in Lisbon, Portugal, discuss the results of the ORIOLE trial in the context of other trials of patients with oligometastatic prostate cancer.
Summing up their observations, the commentators believe there is support for the hypothesis “that all detectable oligometastatic lesions should be systematically ablated, if feasible, in an effort to maximize oligometastatic cancer cure.”
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