Background: AMP-224, a B7-DC Fc fusion protein, binds to PD-1, an inhibitory receptor that is present on the cell surface of exhausted, activated, effector, and memory T cells. AMP-224 has a unique mechanism of action in that it binds specifically to PD-1^HI T cells (chronically stimulated / exhausted T cells) but not to PD-1^LOcells which represent the normal activated T cell population. Several preclinical studies have documented an increase in peripheral antitumor immunity following radiation, a phenomenon known as the “abscopal effect”. Tumor PD-L1 expression has also been shown to be induced by radiation, which can suppress the anti-tumor immune response. Inhibition of PD-1/PDL-1 axis has been shown to improve anti-tumor immunity by blocking the tumor-mediated suppression of cytotoxic T cells. The aim of the study is to evaluate whether the anti-tumor immunity of anti-PD1 therapy (with AMP-224) can be enhanced by radiation therapy. Methods: Patients with histologically confirmed metastatic colorectal cancer to liver are being enrolled to this pilot study. The objectives are to determine the safety, tolerability and feasibility of AMP-224 in combination with stereotactic body radiation therapy (SBRT) to metastatic hepatic metastasis in patients with advanced colorectal cancer. Select eligibility are as follows: at least 1 measurable metastatic hepatic lesion by RECIST 1.1 criteria and amenable to SBRT. Patient must have progressed on or been intolerant of at least one prior oxaliplatin- and/or irinotecan-containing regimen and have metastatic lesions that are not amenable to curative resection; ECOG ≤ 1; Life expectancy of greater than 3 months. Acceptable organ and bone marrow function. No active or prior documented autoimmune or inflammatory disorders. Clinical trial information: awaited.