Inclusion Criteria
Confirmed colorectal adenocarcinoma, with unresectable metastatic or locally advanced disease
Previously received 1-2 prior lines of therapy
Females of childbearing potential must have a negative serum pregnancy test within 24 hours prior to receiving the first dose of study medication. Females of childbearing potential must agree to use 2 methods of effective contraception or abstain from heterosexual sex throughout the treatment period and for 5 months after the last dose of study treatment. Females of childbearing potential are women who have not been surgically sterilized (have undergone a hysterectomy, bilateral tubal ligation, or bilateral oophorectomy) or have not been free of menses for >1 year.
Male subjects with female partners must have had a prior vasectomy or agree to use an adequate method of contraception (i.e., double barrier method: condom plus spermicidal agent) starting with the first dose of study therapy through 7 months after the last dose of study treatment.
Exclusion Criteria
Past treatment with an antibody targeting EGFR including cetuximab or panitumumab.
Past treatment with an antibody targeting immune checkpoints including CTLA-4, PD-1, PD-L1, PD-L2, or CD137.
Known untreated brain metastasis or brain metastasis treated within 3 months prior to enrollment in this trial.
Has evidence of interstitial lung disease or active, non-infectious pneumonitis.
Has a known additional malignancy that is active and/or progressive requiring treatment; exceptions include basal cell or squamous cell skin cancer, in situ cervical or bladder cancer, or other cancer for which the subject has been disease- free for at least five years.
Treatment within 21 days of the first dose of study drug with any other chemotherapy, immunotherapy, biologic therapy, vaccine therapy, or investigational treatment for the treatment of malignancy, or failure to recover from adverse effects of prior therapies administered over 4 weeks prior to Study Day 1. All toxicities from prior therapies must be ? Grade 1 (or ? Grade 2 for alopecia or peripheral neuropathy)
Any serious and/or unstable pre-existing medical disorder (aside from malignancy exception above), psychiatric disorder, or other conditions that could interfere with subject?s safety, obtaining informed consent, or compliance to the study procedures.
Pregnant or breastfeeding, or planning to become pregnant within 6 months after the end of treatment. (NOTE: breast milk cannot be stored for future use while the mother is being treated on study).
History of organ allograft or other history of immunodeficiency, or is receiving systemic steroid therapy or any other form of immunosuppressive therapy within 7 days before the first dose of investigational treatment.
Inability or unwillingness to comply with study and/or follow-up requirements.
Any major surgery, extensive radiotherapy, chemotherapy with clinically significant delayed toxicity, biologic therapy, or immunotherapy within 21 days prior to randomization and/or daily or weekly chemotherapy without the potential for delayed toxicity within 14 days prior to randomization.
Known immediate or delayed hypersensitivity reaction or idiosyncrasy to drugs chemically related to study drug.
Known Human Immunodeficiency Virus (HIV), Hepatitis B virus (HBV), or Hepatitis C virus (HCV) infection. Subjects with laboratory evidence of cleared HBV and HCV infection will be permitted.
Active autoimmune disease requiring systemic treatment in the past 3 months (for example with disease modifying agents, corticosteroids, or immunosuppressive drugs). Replacement therapy (eg, thyroxine, insulin, or physiologic corticosteroid replacement therapy for adrenal or pituitary insufficiency, etc.) is not considered a form of systemic treatment. Subjects with vitiligo or resolved childhood asthma/atopy would be an exception to this rule. Subjects that require intermittent use of bronchodilators, local steroid injections, or inhaled or topical steroids would not be excluded from the study. Subjects with hypothyroidism stable on hormone replacement or Sjogren's syndrome will not be excluded from the study.
Active infection requiring intravenous systemic therapy.

Participants will not be paid for their participation.