Is local ablative stereotactic radiation therapy a valuable rescue strategy for time on drug in patients enrolled in phase I trials?

ABSTRACT

BACKGROUND: Patients with advanced tumours enrolled in phase I trials display strong treatment expectations and few therapeutic alternatives. When oligo-acquired resistance (≤3 lesions of disease progression; OAR) occurs, local ablative stereotactic radiotherapy (SRT) could allow disease control and continuing the experimental systemic treatment. PATIENTS AND METHODS: Data from patients enrolled in phase I trials evaluating systemic treatments, who experienced OAR while on the phase I systemic therapy and subsequently received SRT between 01/2014-04/2023 were retrospectively analysed. PFS1 (trial entry to OAR), PFS2 (SRT to first subsequent relapse), time to next systemic treatment (TTNT), and OS were assessed. First subsequent patterns of relapse after SRT were distinguished as OAR2, which could be locally rechallenged, or systemic acquired resistance (>3 lesions of disease progression; SAR). When available, correlations between molecular profile and pathway enrichments of OAR and SAR were explored. RESULTS: Forty-two patients with 52 oligoprogressive lesions were analysed. The median follow-up was 24 months. SRT allowed a median PFS2 of 7.1 months and a median TTNT of 12.8 months. PFS2 included 49% OAR2 and 51% SAR. Median time to first subsequent relapse (9.6 months vs 3.5 months, P=0.014) and TTNT (22.4 months vs 7.6 months, P<0.001) were longer for OAR2 as compared to SAR. No severe toxicities were reported. A PFS1 <6 months and de novo oligoprogressive lesions associated with the presence of SAR. More diverse enriched gene pathways were observed for SAR as compared to OAR2. CONCLUSION: In patients enrolled in phase I trials, OAR managed with SRT may increase time on investigational systemic treatments. Predictive factors reflecting tumour aggressiveness and clonal heterogeneity could help deciphering OAR2 from SAR and maximize SRT output in the oligoprogressive setting.