Prolonged pemetrexed infusion plus gemcitabine in refractory metastatic colorectal cancer: Preclinical rationale and phase II study results

Background. We investigated the cytotoxic activity of pemetrexed in combination with several drugs (gemcitabine, carboplatin, vinorelbine, and mitomycin C) using different exposure schedules in three colon cancer cell lines. The best results were obtained with the following schedule: a prolonged pemetrexed exposure followed by a 48-hour wash-out and then gemcitabine. This combination was then advanced to a phase II clinical trial. Methods. Patients with metastatic colorectal cancer in progression after standard treatment were included in the study. Adequate bonemarrow reserve, normal hepatic and renal function, and an Eastern Cooperative Oncology Group (ECOG) performance status of 0-2 were required. Treatment consisted of an 8-hour intravenous infusion of pemetrexed 150 mg/m² on day 1 and a 30-minute intravenous infusion of gemcitabine 1,000 mg/m² on day 3 of each cycle, repeated every 14 days. Results. Fourteen patients were enrolled onto the study (first step). No objective responses were seen, and evidence of stable disease was observed in only one of the 12 evaluable patients. The most important grade 3-4 side effects were hematological toxicity (neutropenia 64.2%, thrombocytopenia 71.4%, anemia 28.7%), fatigue (50.0%), and stomatitis (21.5%). Median overall survival and time to progression were 5.8 months (95% confidence interval [CI]: 3.9-7.1) and 2.1 months (95% CI: 1.7-2.8), respectively. Conclusion. The experimental pemetrexed-gemcitabine combination proved to be inactive and moderately toxic.