During this study patients will receive treatment of omeprazole at the dose depending on group enrollment
* Group A will receive omeprazole 80 mg, twice a day for 12-14 days unless unacceptable toxicity
* Group B, will receive omeprazole 20 mg, once a day for 12-14 days
Patients will receive treatment for 2\~3 weeks during the study, and 2 months of follow up.
Total accrual is anticipated to take 2 years.
