Combination Chemotherapy With or Without Vismodegib in Treating Patients With Advanced Stomach Cancer or Gastroesophageal Junction Cancer

Inclusion Criteria

• Patients must have histologically or cytologically confirmed gastric or gastroesophageal junction (GEJ) adenocarcinoma not amenable to surgical resection
• Patients must have measurable disease, defined as at least one lesion that can be accurately measured in at least one dimension (longest diameter to be recorded) as >= 20 mm with conventional techniques or as >= 10 mm with spiral computed tomography (CT) scan
• No prior chemotherapy for advanced disease; patients may have receive adjuvant chemotherapy or chemoradiation if > 6 months has elapsed since completion of treatment
• Life expectancy of greater than 3 months
• Eastern Cooperative Oncology Group (ECOG) performance status 70%)
• Absolute neutrophil count >= 1,500/mcL
• Platelets >= 100,000/mcL
• Total bilirubin = = 60 mL/min/1.73 m^2 for patients with creatinine levels above institutional normal
• Baseline imaging studies performed = 45 years old
• Ability to understand and the willingness to sign a written informed consent document

Exclusion Criteria

• Patients who have had chemotherapy or radiotherapy within 6 months prior to entering the study
• Patients may not be receiving any other investigational agents
• Patients with known brain metastases should be excluded from this clinical trial
• History of allergic reactions attributed to compounds of similar chemical or biologic composition to GDC-0449, 5-fluorouracil or oxaliplatin
• GDC-0449 inhibits cytochrome P450, family 2, subfamily C, polypeptide 8 (CYP2C8), cytochrome P450, family 2, subfamily C, polypeptide 9 (CYP2C9), and cytochrome P450, family 2, subfamily C, polypeptide 19 (CYP2C19) drug metabolism enzymes in vitro at concentrations that may be clinically relevant; therefore, caution should be exercised when dosing GDC-0449 concurrently with medications that are substrates of CYP2C8, CYP2C9, and CYP2C19 and have narrow therapeutic windows
• Patients with malabsorption syndrome or other condition that would interfere with intestinal absorption
• Patients unable to swallow whole capsules
• Patients with clinically active liver disease, including viral or other hepatitis or cirrhosis are ineligible
• Patients with uncontrolled hypocalcemia, hypomagnesemia, hyponatremia or hypokalemia defined as less than the lower limit of normal for the institution, despite adequate electrolyte supplementation are excluded from this study
• Pre-existing > grade 1 peripheral sensory neuropathy
• Previous or concurrent malignancy; exceptions: treated basal cell or squamous cell skin cancer, in situ cervical cancer, or lobular carcinoma in situ in one breast; or other cancer which the patient has been disease-free ≥5 years
• Uncontrolled intercurrent illness including, but not limited to, ongoing or active infection, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with study requirements
• Pregnant women are excluded from this study; breastfeeding should be discontinued if the mother is treated with GDC-0449
• Human immunodeficiency virus (HIV)-positive patients on combination antiretroviral therapy are ineligible