Tolerability and response of palliative radiotherapy in patients receiving tumor-infiltrating lymphocyte therapy.

e14527 Background: Tumor-infiltrating lymphocyte (TIL) therapy is an emerging therapeutic option for patients with metastatic tumors having progressed on multiple lines of systemic therapy. It is unknown how TIL therapy impacts the tolerability and effectiveness of palliative radiotherapy (RT). We herein present a case series of patients having received both TIL therapy and palliative RT along with the associated local responses and toxicity profiles. Methods: A single institution retrospective database review identified patients treated with TIL therapy following progression on ≥2 standard treatment(s) for metastatic disease. Patients were eligible for inclusion if they received palliative radiotherapy treatment within 1 year of TIL delivery as pre- or post-TIL therapy. Patient demographic data was collected and descriptive statistics reported. Radiographic imaging response was assigned in accordance with Response Evaluation Criteria in Solid Tumors (RECIST). Toxicities were graded in accordance with Common Terminology Criteria for Adverse Events (CTCAE) Version 5.0. Results: Between 2017–2021, a total of 10 patients receiving TIL therapy treated across 12 courses of palliative RT were included for analysis. 8 of 10 patients (80%) had a primary diagnosis of malignant melanoma and 2 (20%) had non-small cell lung cancer. RT was administered to 7 patients pre- and 3 patients post-TIL therapy. Within the pre-TIL cohort, 2 patients received RT between TIL harvest and infusion. Patients received an average total dose of 26 Gy (range, 8-45 Gy). Median patient follow-up after RT was 6 months. Of the patients who received RT prior to TIL therapy, 6 of 9 sites demonstrated at-least stable disease at the site of RT versus 1 of 3 sites receiving post-TIL RT. Across the cohort, 2 patients experienced Grade 1 toxicities associated with RT treatment. No Grade 2+ events were reported. Conclusions: Palliative RT appears to be safe and tolerable when delivered both prior to and post-TIL therapy. RT may be an option for bridging therapy between TIL harvest and infusion. Local response rates to RT were greater in patients receiving RT prior to TIL infusion. Further investigations are warranted to determine the optimal dose, fractionation, and timing of RT when integrating it into future TIL therapy protocols. [Table: see text]