Therapeutic uses of topotecan for thoracic malignancies

Topotecan, a topoisomerase 1 inhibitor (topo1-i), is a semi-synthetic derivative of camptothecan with well-established cytotoxic properties. It is licensed for the treatment of relapsed, sensitive small cell lung cancer (SCLC) and for second line treatment in ovarian cancer. Studies have also shown this drug to be an effective first line treatment for SCLC with either cisplatin or in combination with a topoisomerase 2 inhibitor (topo2-i), etoposide; both combinations have shown similar efficacy. Oral and parenteral formulations of topotecan have proven to be equivocal in relapsed SCLC patients. The parenteral form showed reduced rates of severe haematological toxicities and better symptom control than an anthracycline combination (CAV). In relapsed SCLC, a randomised phase III trial of oral topotecan versus best supportive care showed a statistically significant increase in overall survival. In the second line treatment of non-small cell lung cancer (NSCLC), oral topotecan was not inferior to the current standard iv docetaxel for 1 year survival rates. Worthwhile potential investigations include combining oral topotecan with other oral agents to design treatments for different lines of therapy. The new oral formulation of topotecan also lends itself to testing with small molecule tyrosine kinase inhibitors. The myelosuppressive toxicity profile needs to be vigorously monitored and managed. The trials with oral topotecan have also highlighted the need to reassess the utility of the terms ‘sensitive’ and ‘resistant’ in the selection of patients with relapsed small cell lung cancer.