Prolonged infusion of gemcitabine in stage IV breast cancer: a phase I study

Gemcitabine is an effective agent in the treatment of metastatic breast cancer. The phosphorylation of gemcitabine into the active gemcitabine triphosphate (dFdCTP) is catalyzed by deoxycytidine kinase. This enzyme is saturated at plasma concentrations achieved after an infusion over 30 min. Therefore accumulation of higher intracellular dFdCTP concentrations, which may result in an enhanced antineoplastic activity, cannot be achieved by higher dosage, but only by prolonged infusion time. The objectives of this phase I trial were to determine the dose-limiting toxicities (DLT) and the maximum tolerated dose (MTD) of gemcitabine given as a 6 h i.v. infusion. Patients with metastatic breast cancer were treated with gemcitabine as a 6 h infusion on days 1, 8 and 15 every 4 weeks. The starting dose was 200 mg/m2 with an interindividual escalation in 50 mg/m2 increments. Sixteen patients received 196 doses through three dose levels. All patients were assessable for toxicity, 13 assessable for response. The MTD was 250 mg/m2. DLT was observed at 300 mg/m2 consisting of a reversible elevation of transaminases WHO grade 3 in two patients and cutaneous toxicity grade 3 in one patient. Most common non-hematologic toxicities were mild to moderate and rapidly reversible elevation of liver enzymes in all patients, nausea and vomiting (four patients grade 2, five patients grade 3), and mild alopecia. Hematologic toxicity was mild with neutropenia WHO grade 3 and 4 in only one patient each, and no grade 3 thrombocytopenia. One patient achieved a complete remission and another patient a partial response, for an overall response rate of 15% (two of 13). In addition, seven patients (54%) had stable disease and four (31%) failed to respond to the treatment. We conclude gemcitabine 250 mg/m2 days 1, 8 and 15 every 4 weeks can be safely administered as 6 h infusion. Toxicity, especially myelosuppression, is surprisingly mild. Based on this result a phase II study with 250 mg/m2 administered over 6 h was initiated to determine the efficacy.