Salvage Treatment With Topotecan in Patients With Irinotecan-Refractory Small Cell Lung Cancer

Current commonly used second-line approaches for SCLC include re-induction with first-line therapy for chemosensitive disease, or single-agent topotecan. Although the efficacy of topotecan as second-line chemotherapy for SCLC has been consistently demonstrated in a number of clinical studies, the choice of irinotecan as first-line therapy prevented use of the evidence-based option such as topotecan. Topotecan and irinotecan are cytotoxic agents that inhibit same intracellular pathway, namely topoisomerase I, which is an enzyme involved in DNA replication and RNA transcription.

Although their mechanism of action is similar, the preclinical and clinical data of these two drugs have some notable differences. Topotecan and irinotecan have different spectra of antitumor activity in various models of human cancer. Clinical data support that these agents may have different spectra of activity. The differences in antitumor activities may also reflect different mechanisms of resistance. Furthermore, topotecan and irinotecan have different limiting toxicities (myelosuppression and diarrhea, respectively).