New agents in the treatment of small-cell lung cancer: focus on gemcitabine.

Small-cell lung cancer (SCLC) accounts for 20%-25% of all new cases of lung cancer and represents the sixth most commonly diagnosed cancer in the United States. Given the tumor's systemic nature and chemoresponsiveness, chemotherapy has become the cornerstone of its management. Chemotherapy significantly prolongs survival; however, most of the patients still die within 2 years of diagnosis. Combination chemotherapy represents the treatment of choice for this disease. In the United States, cisplatin/etoposide is the regimen most frequently used for the first-line therapy of SCLC patients because of its better therapeutic index. Upon recurrence, topotecan is the Food and Drug Administration-approved treatment based on a phase III trial that showed no statistically significant differences in survival or response for topotecan compared with CAV (cyclophosphamide/doxorubicin/vincristine) but a better disease-related symptom improvement compared to baseline favoring the topoisomerase I inhibitor. Newer agents, with novel mechanisms of action, have shown activity against SCLC and are being tested in many different combinations. Among these agents, gemcitabine has attractive mechanisms of action and toxicity profile. Gemcitabine is a pyrimidine nucleoside antimetabolite, analogue to cytosine arabinoside, which through incorporation into the DNA leads to inhibition of DNA synthesis and cytotoxicity. As a single agent, gemcitabine has modest activity against SCLC. However, like with many other drugs, response rates improve when gemcitabine is used in combination regimens. Phase II and III studies of combinations with classic drugs for the management of SCLC patients such as cisplatin and/or etoposide and gemcitabine demonstrate comparable results to those of standard therapies. The gemcitabine/paclitaxel and gemcitabine/topoisomerase I inhibitor combinations are also of great interest, and preliminary results in previously treated patients are promising. The proper role of gemcitabine in the treatment of patients with SCLC awaits future testing in randomized phase III trials.