Inclusion Criteria:

- Patient has histologically or cytologically confirmed, unresectable and/or metastatic
GIST

- Patient has measurable disease

- Patient has documented objective progression following, or intolerance to, treatment
with both imatinib and sunitinib

- Patient's Eastern Cooperative Oncology Group (ECOG) performance status is 0 to 2

- Patient has either:

1. prior results from KIT and PDGFRα mutation analysis that meet analytical
criteria as defined for the on-study analysis of these mutations and tumor
tissue (from either primary or metastatic tumor)that can be submitted for
analysis within 30 days after the first dose of study therapy; or

2. if prior results from KIT and PDGFRα mutation analysis are not available or do
not meet analytical criteria as above, then tumor tissue (from either primary or
metastatic tumor) must be submitted for genotype testing at the latest 28 days
prior to the first dose of study therapy

- Patient has adequate hematologic, hepatic, renal and coagulation function

- Women of childbearing potential and sexually active males must agree to use adequate
contraception prior to study and for at least 12 weeks after the last dose of IMC-3G3

- Patient has a life expectancy of ≥ 3 months

Exclusion Criteria:

- Patient has untreated central nervous system metastases, and as a result, is
clinically unstable with regard to neurologic function

- Patient has a history of another primary cancer

- Patient has received any investigational therapy within 14 days prior to
registration, or is currently enrolled in any other type of medical research

- Patient is receiving concurrent treatment with other anticancer therapy

- Patient has known immunodeficiency virus (HIV) infection

- Patient has undergone major surgery within 28 days prior to registration

- If female, patient is pregnant or breastfeeding