Objective: Previous studies have demonstrated the ability of non-lethal doses of radiation to alter the phenotype of tumor cells to facilitate immune mediated killing. This pilot study evaluated the tolerability of a vector-based vaccine targeting carcinoembryonic antigen (CEA) in combination with radiation therapy in patients with gastrointestinal malignancies metastatic to the liver.
Methods: Patients enrolled had progressive CEA(+) tumors with metastatic liver lesions. Patients had received a median of three previous chemotherapy regimens, with a median of 2 months since their last chemotherapy regimen. Only 58% had metastatic disease limited to the liver. Vaccination commenced day 1 with biweekly boosters and split-course radiation (total 32 Gy) starting on day 21. Blood was collected at baseline and day 91 for immunological analysis.
Results/conclusion: A total of 12 patients were enrolled. There were no grade 3 or greater toxicities or grade 2 or greater hepatic toxicities. Median time on-study was 3 months, with the longest time on treatment being 5 months (n = 2). Immunological analysis was limited to two patients; neither showed an increase above baseline in CEA-specific T cells post-therapy. CEA/TRICOM vaccination in combination with low-dose radiation therapy is safe. There was limited evidence of activity in this patient population.