Gemcitabine: single-agent and combination therapy in non-small cell lung cancer.

With the advent of several newer agents with single-agent response rates greater than 20% and approximately 30%-40% in combination therapy, non-small cell lung cancer (NSCLC) may now be considered a malignancy that is moderately sensitive to chemotherapy. Examples of these agents include the taxanes, paclitaxel and docetaxel; vinorelbine, a new vinca alkaloid, and the camptothecins, of which CPT-11 is the most actively studied agent. Another new and exciting agent is gemcitabine, a nucleoside analogue structurally related to cytosine arabinoside. Gemcitabine's mechanism of action is activated by deoxycytidine kinase to dFdCMP, dFdCDP and dFdCTP. The latter two compounds, when incorporated into DNA, result in chain termination. Phase I studies using a short infusion schedule given weekly for three weeks followed by one week off established 1,000-1,250 mg/m2/week as the maximum tolerated dose. Single-agent gemcitabine has been extensively studied in patients with chemotherapy-naïve advanced NSCLC with response rates of approximately 20%. Response rates for the combination of gemcitabine plus cisplatin are approximately 28%-54% in phase II trials. Recently, this combination has been studied in randomized phase II and III trials revealing improvements in response rates, time to progression and, in the phase III trial, survival. Current and future studies are evaluating gemcitabine in non-cisplatin combinations (i.e., taxanes).