Immunotherapy SBRT Sensitization of the Programmed Death-1 (PD-1) Effect

Blockade of the PD-1/PD-L1 T-cell checkpoint pathway is an effective and well tolerated approach to stimulating the immune response which is a critical option in the treatment of metastatic NSCLC. However, progression free survival (PFS) is increased by only 2-4 months and median overall survival (OS) by 3-9 months. There is compelling evidence that PFS is increased up to 3 fold and OS by 2 fold in patients receiving a course of radiation therapy while on immunotherapy. Radiotherapy is known to induce immunogenic tumor cell death and upregulation of dendritic cells and antigen presentation leading to activation of cytotoxic T-Cells. Dramatic T-cell activation has been demonstrated where tumor regression occurs outside the radiation treatment field in a phenomenon termed the abscopal effect and is associated with high dose radiation delivered via SBRT. As such, SBRT activation of T-cells could be complementary to immunotherapy and enhance T-cell mediated killing via PD-L1 blockade which could lead to lasting and durable tumor response with improved progression free survival and overall survival.