Inclusion Criteria:

          -  Age ≥18 years

          -  Histological or cytological confirmation of colorectal cancer with metastasis to the
             liver. Mismatch repair or microsatellite instability status of the tumor needs to be
             known. Tumors need to be mismatch repair proficient (for mismatch repair deficient
             tumors immunotherapy is already approved).

          -  Patient must have at least 1 liver lesion measurable as defined in the protocol

          -  Must have liver metastases and be appropriate for treatment with Y-90
             radioembolization therapy as determined by the treating medical oncologist and
             interventional radiologist/oncologist, and nuclear medicine physician(s). NOTE: the
             goal of therapy is safety and parenchymal sparing. Typically, since the treatment is
             personalized, the goal is to have at least 30% liver parenchymal sparing post
             treatment.

          -  Must have a metastatic focus amendable to biopsy. It is permissible to use same or
             alternative lesion for biopsy for assessment for tumor response and changes in
             microenvironment (mandatory pre- and post-Y90-RE biopsy).

          -  At least 2 but no more than 3 lines of therapy allowed in metastatic setting. These
             include at least treatment with a fluoropyrimidine, oxaliplatin, and/or
             irinotecan-based therapy, an anti-VEGF therapy and, if RAS wild-type, an anti-EGFR
             therapy, unless deemed intolerant or not suitable by the treating oncologist. NOTE:
             adjuvant and/or maintenance chemotherapy does not count as an additional line of
             therapy. (Patients with more than 3 lines of therapy are at risk for liver disease
             from prior systemic therapies and would not be reasonable candidates for Y90-RE).

          -  ECOG Performance Status (PS) 0 or 1.

          -  Negative serum pregnancy test done ≤7 days prior to registration, for persons of
             childbearing potential only.

          -  Females of childbearing potential (FOCBP), must use appropriate method(s) of
             contraception. FOCBP are defined as those who are not surgically sterile (i.e.,
             bilateral tubal ligation, bilateral oophorectomy, or complete hysterectomy) or
             postmenopausal (defined as 12 months with no menses without an alternative medical
             cause). Additionally, FOCBP must agree to follow instructions for method(s) of
             contraception for the duration of treatment with durvalumab plus 5 half-lives of
             durvalumab (13 weeks) plus 30 days (duration of ovulatory cycle) for a total of 17
             weeks post-treatment completion (details in appendix).

          -  Men who are sexually active with FOCBP must agree to follow instructions for method(s)
             of contraception for the duration of treatment with durvalumab plus 5 half-lives of
             durvalumab plus 90 days (duration of sperm turnover) for a total of 25 weeks
             post-treatment completion (details in appendix).

          -  Provide written informed consent.

          -  Ability to complete questionnaire(s) by themselves or with assistance.

          -  Willingness to provide mandatory blood specimens for correlative research (detailed in
             protocol).

          -  Willingness to provide mandatory tissue specimens for correlative research (detailed
             in protocol). NOTE: If tissue is deemed inaccessible, patient cannot participate in
             study.

          -  Willingness to return to enrolling institution for follow-up (during the Active
             Monitoring Phase of the study).

          -  Must have a life expectancy of at least 6 months.

        Exclusion Criteria:

          -  Any of the following laboratory abnormalities:

               -  Hemoglobin <8.0 g/dL

               -  Absolute neutrophil count (ANC) <1500/mm3

               -  Platelet count <100,000/mm3

               -  Total bilirubin >1.5 x ULN (except in subjects with Gilbert Syndrome, who cannot
                  have a total bilirubin > 3.0 mg/dL)

               -  Alanine aminotransferase (ALT) and Aspartate transaminase (AST) >2.5 x ULN

               -  Serum creatinine > 1.5 x ULN OR

               -  Calculated creatinine clearance <30 ml/min using the Cockcroft-Gault formula

          -  Any of the following because this study involves an agent that has known genotoxic,
             mutagenic and teratogenic effects:

               -  Pregnant persons

               -  Nursing persons

               -  Persons of childbearing potential who are unwilling to employ adequate
                  contraception

          -  Co-morbid systemic illnesses or other severe concurrent disease which, in the judgment
             of the investigator, would make the patient inappropriate for entry into this study or
             interfere significantly with the proper assessment of safety and toxicity of the
             prescribed regimens.

          -  Untreated central nervous system (CNS) metastatic disease (including spinal cord and
             leptomeningeal disease). NOTE: Patients with previously treated CNS metastases that
             are radiographically and neurologically stable for ≥ 6 weeks are permitted.

          -  Uncontrolled intercurrent illness including, but not limited to, autoimmune disease,
             ongoing or active infection, or psychiatric illness/social situations that would limit
             compliance with study requirements. EXCEPTION: Patients who have adequately controlled
             autoimmune disease with or without medications are permitted as long as deemed
             reasonable by treating physician.

          -  Received any other investigational agent incorporating chemotherapy and/or biologics
             within 14 days prior to first dose of durvalumab which would be considered as a
             treatment for the primary neoplasm. For patients on active treatment, last treatment
             and 1st dose of Durvalumab should be at least ≥ 14 days. EXCEPTION: Other forms of
             concurrent observational studies are permitted.

          -  Other active malignancy ≤3 years prior to registration. EXCEPTIONS: Non-melanoma skin
             cancer, lentigo maligna- in-situ, or carcinoma-in-situ of the cervix. Also prior
             malignancy already treated with curative intent and with no known active disease
             present would be considered eligible.

          -  History of unstable cardiac disease defined as one of the following:

               -  Congestive heart failure > class II New York Heart Association (NYHA). (Appendix
                  II)

               -  Unstable angina (angina symptoms at rest) or new onset angina (began ≤ 3 months
                  prior to registration)

               -  Myocardial infarction ≤ 3 months

               -  Uncontrolled cardiac ventricular arrhythmias. EXCEPTION: Subjects that are stable
                  on anti-arrhythmic therapy are eligible.

          -  Any concurrent chemotherapy, biologic, or hormonal therapy for cancer treatment within
             14 days of first dose of durvalumab. NOTE: Subjects can be screened during washout
             period.

          -  History of severe allergic reactions (i.e. Grade 4 allergy, anaphylactic reaction from
             which the subject did not recover ≤ 6 hours of initiation of supportive care)

          -  Failure to recover from toxicities from prior anti-cancer therapy, defined as having
             not resolved to National Cancer Institute (NCI) CTCAE version 5.0 Grade ≤ 1.
             EXCEPTIONS: Alopecia and laboratory values listed per the exclusion criteria. Also
             subjects with irreversible toxicity that is not reasonably expected to be exacerbated
             by any investigational products (i.e. hearing loss) will be permitted.

          -  Use of steroids. EXCEPTIONS: Systemic glucocorticoids will be permitted as long as it
             is ≤20 mg of prednisone equivalent. Topical steroids, such as bronchodilators and
             local steroid injections are also permitted if clinically required.

          -  Patients with renal failure currently requiring dialysis of any kind.

          -  Active HIV, Hepatitis B or C with uncontrolled disease. EXCEPTION: Patient with
             non-active, controlled disease will be allowed to participate in study. NOTE: A
             detailed assessment of HIV and Hepatitis B/C medical history must be done at screening
             for all patients. HIV 1/2 antibodies, HBsAg and HCV Ab Screen w/Reflex testing are
             required at screening for all patients.

          -  Patients weighing <30kg will be excluded from enrollment

          -  History of allogenic organ transplantation