ESTRO 2024 - Abstract Book

S1852

Clinical - Mixed sites, palliation

ESTRO 2024

criterion was the initiation of other systemic therapies during the analysed period. We assessed the rate of AbE based on NIL measurements, categorised as Abscopal Response (AR), Abscopal Progression (AP), or Abscopal Control (AC), according to the iRECIST criteria. Further endpoints included overall survival (OS), progression-free survival (PFS), and RT-ICI schemes. For the primary endpoint, we hypothesized an AbE rate of 20%, sample size calculation required 62 patients for 10% precision. Figure 1 shows the conduct of the study.

Results:

We screened 3,464 and identified 98 eligible patients, predominantly male (n=63, 64%) with a median age of 60 (range 18-81) years and UICC stage IV (100%) at the time of treatment. Non-small cell lung cancer (NSCLC, n=32, 33%) and malignant melanoma (n=30, 31%) were the most common tumour entities, nivolumab was the most applied ICI (n=48, 49%), and hypofractionation the most commonly used fractionation scheme (n=55, 56%). After 3 months follow-up, 41% of patients (n=40) showed a clinical benefit (complete response, partial response or stable disease), 19% (n=19) had a mixed response, and 38% (n=37) had progressive disease. AbE assessment revealed that 38% (n=37) of patients had at least one NIL with AR, of which 57% (n=21) had complete AR in all NILs.

Median OS for all patients was 11 (range 1-62) months. Patients with complete AR showed a median OS of 17 (range 1-60) months and with AC (n=29) 14 (range 1-62) months, whereas patients with no abscopal benefit (AP, no AR, no