3006 - Efficacy and Safety of Concurrent Radioimmunotherapy for Locally Advanced and Metastatic Cutaneous Squamous Cell Carcinoma

A. Kassardjian¹, C. J. Ladbury¹, A. Tam¹, Y. Xing², B. Modi³, V. Villaflor⁴, S. Maroongroge⁵, T. Loh⁶, and A. Amini¹; ¹Department of Radiation Oncology, City of Hope National Medical Center, Duarte, CA, ²Department of Medical Oncology, City of Hope National Medical Center, Duarte, CA, ³Department of Dermatology, City of Hope National Medical Center, Duarte, CA, ⁴Department of Medical Oncology and Therapeutics Research, City of Hope National Medical Center, Duarte, CA, ⁵Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, ⁶City of Hope, Duarte, CA

Purpose/Objective(s): Concurrent use of radiation therapy (RT) and immune checkpoint inhibitors (ICI) for locally advanced and metastatic cutaneous squamous cell carcinoma (cSCC) is not well understood. This study examines a retrospective cohort of patients with cSCC treated with RT and ICI and reports rates of tumor control, survival, and toxicity. We hypothesize that combined use of RT and ICI for cSCC results in favorable oncologic outcomes and safety profile. Materials/

Methods: We examined patients at a single comprehensive cancer center receiving concurrent ICI and RT between April 2019 and July 2022. Patients were stratified based on disease stage. Locoregional control (LRC), freedom from distant metastases (FFDM), progression-free survival (PFS), and overall survival (OS) were analyzed at 1 year and 2 years upon completion of RT. Statistical analysis and comparison between groups were performed using Kaplan-Meier or Fine-Gray competing risk survival analyses. Toxicities were tabulated by the Common Terminology Criteria for Adverse Events (CTCAE v4.0).
Results: Thirteen patients with locally advanced (53.8%) or metastatic (46.2%) cSCC received concurrent RT and ICI therapy with cemiplimab (84.6%) or pembrolizumab (15.4%). Median age was 77 years [range 65-92]. RT was delivered to the head and neck (61.5%) or body (38.5%). Radiation dose ranged from 55 to 70 Gy for intensity-modulated radiotherapy (IMRT) (69.2%), and 30 to 40 Gy for stereotactic body radiotherapy (SBRT) (30.8%). Median follow-up was 15.4 months, and outcomes were analyzed at 12 and 24 months (Table 1). Locally advanced patients had significantly greater LRC (p<0.001) compared to metastatic patients. Other outcomes were not significant. One patient (7.7%) developed grade 3 skin dermatitis, and there was no report of grade 4+ toxicities.
Conclusion: Concurrent use of ICI and RT was safe and effective in our cohort of patients with cSCC. Limited toxicities were observed, and tumor control may be more pronounced in locally advanced compared to metastatic patients. Additional studies are necessary to further explore the relationship of RT and ICI therapy, and whether their concurrent use improves oncologic outcomes without compromising tolerability.

Abstract 3006 –Table 1. Outcomes of concurrent ICI and RT for cSCC at 1 and 2 years (yr) in locally advanced (7), metastatic (6), and total (13) patients.

Category	Locally Advanced Median % [95% CI]	Metastatic Median % [95% CI]	Total Median % [95% CI]
1-yr LRC	100% [100-100%]	100% [100-100%]	100% [100-100%]
1-yr FFDM	100% [100-100%]	66.3% [37.8-100%]	83.8% [65.6-100%]
1-yr PFS	68.6% [40.3-100%]	50.0% [22.5-100%]	59.8% [37.8-94.7%]
1-yr OS	68.6% [40.3-100%]	83.3% [58.3-100%]	75.2% [54.2-100%]
2-yr LRC	100% [100-100%]	56.3% [19.6-100%]	84.3% [60.6-100%]
2-yr FFDM	76.6% [45.7-100%]	49.3% [22.3-100%]	62.4% [39.0-99.8%]
2-yr PFS	45.7% [17.5-100%]	0.0% [0-0%]	25.6% [8.3-78.9%]
2-yr OS	68.6% [40.3-100%]	41.7% [10.0-100%]	62.7% [38.6-100%]