Patients with colorectal cancer that had metastatic lesions after been treated with definitive surgery or chemoradiotherapy are being asked to participate in this study. 1. To observe immunity-mediated tumor response outside the radiation field (abscopal effect) after chemoradiotherapy of a metastatic site in metastatic colorectal cancer patients. 2. To induce the efficacy (effectiveness) of a new combination of therapy, chemoradiotherapy and thymalfasin for heavily pretreated, metastatic esophageal cancer patients; 3. To explore the role of PET/CT scanning to assess tumor response/abscopal effect. This study will help find out what abscopal effects (good or bad) the combination of radiotherapy and thymalfasin has on metastatic esophageal cancer.

1. To observe immunity-mediated tumor response outside the radiation field (abscopal effect) after chemoradiotherapy of a metastatic site in metastatic colorectal cancer patients. 2. To induce the efficacy (effectiveness) of a new combination of therapy, chemoradiotherapy and thymalfasin for heavily pretreated, metastatic esophageal cancer patients 3. To explore the role of PET/CT scanning to assess tumor responses/abscopal effect. Eligible are patients with metastatic colorectal cancer who have achieved stable disease or have disease progression after systemic therapy (surgery or definitive chemoradiotherapy) and have at least three separate measurable sites of metastatic lesions. Extent of metastatic disease is recorded both at CT and PET/CT scanning. Radiation is given during combined therapy to one of the lesions, 35Gy in 10 fractions over a two week interval, conformally to maximally spare normal tissue or organ. Thymalfasin treatment is given twice a week with an interval of 3-4 days each week. At day 22 radiation is re-started and the same radiation dose is delivered to a second metastatic site, again with thymalfasin. Abscopal response is evaluated by assessing clinical and PET/CT response in the non-irradiated measurable metastatic sites. A Phase II clinical trial based on an optimum two-stage Phase II Simon design is used to conduct this pilot study. Ten patients will be treated in Stage one; if there are no abscopal responses, the trial will be terminated. If there are one or more abscopal responses in Stage One, the trial will proceed to enroll an additional 19 patients.