Abstract 67P
Background
The abscopal effect (AbE) is a systemic immune response mediated by the effects of radiotherapy (RT) on the immune system. The AbE in patients with metastatic cancer treated with RT alone has been seen rarely, however, in the era of immune checkpoint inhibition (ICI) AbE has been recognized more commonly. The actual frequency in the RT-ICI setting is unclear.
Methods
We retrospectively screened metastatic cancer patients receiving RT for progressive disease during ICI between 2015- 2021. Patients switching systemic treatment within radiological response assessment (RA) were excluded. Eligible patients had ≥1 NIL outside the 10% RT isodose and a maximum of 5 NIL were measured. According to iRECIST, size reduction ≥30% was rated abscopal response (AR), increase by ≥20% abscopal progression (AP), every change of size in between was classified as “control” (abscopal control, AC). Hereby, we report the subgroup of non-small cell lung cancer (NSCLC).
Results
We analyzed preliminary data from 8 participating centers in Germany. 3381 cases were screened to identify 33 eligible NSCLC patients with a total number of 39 lesion irradiated and 85 non-irradiated lesions (NIL). Median age was 63.50 years (interquartile range (IQR): [56.00;67.25]). Patients were treated either with stereotactic (n=3; 9%) or stereotactic fractionated (n=5, 15%), hypofractionated (n=19; 58%) or normofractionated (n=4; 12%) RT or a combination of different fractionations (n=2, 6%). ICI consisted of either pembrolizumab (n=20; 61%) or nivolumab (n=12; 36%). AR as well as AC was found in 9 (27%) patients, respectively. AP and other was seen in 11 (33%) patients. In addition, at least one AR was seen in 4 (12%) patients.
Conclusions
We present the NSCLC subgroup analysis of AbE following concurrent RT for progressive disease during ICI treatment in a large multicenter cohort (ARTIC/ARO 2022-10). We report an AR rate of 27% which is similar to earlier reports ranging between 18-52%. In addition, 12% of the identified NSCLC patients showed at least one AR of the measured NIL. Subgroup analyses, predictors of AbE and survival outcomes from our data are underway.
Legal entity responsible for the study
The authors.
Funding
Has not received any funding.
Disclosure
All authors have declared no conflicts of interest.