The purpose of this study is to evaluate the safety and efficacy of pegamotecan (PEG-camptothecin) in patients with pathologically-diagnosed locally advanced or metastatic adenocarcinoma of the stomach or gastroesophageal junction who have relapsed or progressed following one prior chemotherapy treatment regimen.

Inclusion Criteria:

• Pathologically confirmed diagnosis of adenocarcinoma of the stomach or gastroesophageal junction.
• Disease measurable in at least one dimension.
• Target tumors outside of prior radiation field(s).
• An Eastern Cooperative Oncology Group (ECOG) performance scale score of 0 or 1
• Adequate hematologic profile, as determined by hemoglobin, platelet, and neutrophil count.
• Adequate renal function, as determined by serum creatinine and serum albumin measurements.
• Adequate liver function, as determined by total bilirubin and transaminases levels. Transaminases may be <= 5.0x ULN if due to metastatic disease in the liver.
• Fully recovered from prior surgery.
• No history of hemorrhagic cystitis.
• No microscopic hematuria (>10 RBC/hpf) unless documented to be due to an infection or non-bladder origin.
• Capable of understanding the protocol requirements and risks and providing written informed consent.

Exclusion Criteria:

• Concurrent serious medical illness unrelated to tumor within the past 6 months.
• Known chronic infectious disease, such as AIDS or hepatitis (screening for hepatitis and HIV will not be performed).
• Positive screening pregnancy test or is breast-feeding.
• Female or male subject of reproductive capacity who is unwilling to use methods appropriate to prevent pregnancy during the course of this study.
• Receiving concurrent chemotherapy, investigational agents, radiotherapy, surgery, or has received wide field radiation within the previous 4 weeks.
• History of another malignancy (except basal and squamous cell carcinomas of the skin and carcinoma in situ of the cervix) within the last 5 years.
• Known or clinically suspected brain metastases.
• Received more than one prior regimen of chemotherapy for locally advanced or metastatic adenocarcinoma of the stomach or GE junction.
• Received prior neoadjuvant and/or adjuvant cytotoxic chemotherapy
• Received any investigational drug within the last 30 days.
• Not fully recovered from any prior, and from any reversible side effects related to the administration of cytotoxic chemotherapy, investigational agents, or radiation therapy.
• Prior treatment with a camptothecin analog.