Expression of DNA topoisomerase IIα and topoisomerase IIβ genes predicts survival and response to chemotherapy in patients with small cell lung cancer

Drug resistance is a major problem in patients with small cell lung cancer; in fact, most die of resistant disease, despite an initial response. Several markers of drug resistance have been described in preclinical models, but the mechanism of drug resistance in lung cancer patients remains unknown. The objective of this study was to evaluate the role of the expression of a number of markers of drug resistance, proliferation, and apoptosis in relation to response to chemotherapy and survival in patients with small cell lung cancer. Tumor samples were derived from 93 previously untreated patients who were randomized in a Phase III study to receive cyclophosphamide, epirubicine, and etoposide or cyclophosphamide, epirubicine and vincristine alternating with carboplatin and etoposide. Paraffin-embedded samples, derived from the primary tumor site prior to chemotherapy, were analyzed by immunohistochemistry for expression of markers implicated in drug resistance [topoisomerase (topo) IIα, topo IIβ, and multidrug resistance-associated protein], apoptosis (p53, p21, and bcl-2), or proliferation (Ki67). Response prediction was analyzed by X² test and logistic regression analysis; overall and disease-free survival curves were compared by log-rank test and Cox regression analysis. Shorter survival was observed in patients with extensive disease (P = 0.037) and poorer performance status (P = 0.028) and in patients whose tumors expressed high topo IIα levels (P = 0.01) and high Ki67 (P = 0.024). By multivariate analysis, the following factors were found to be predictive for worse survival: high expression levels of topo IIα, Ki67, and bcl-2; male sex; and extensive disease. High topo IIβ expression was found to be predictive for lower overall and complete response rate. No relationship between apoptotic pathway markers or MRP and response to chemotherapy was observed. In conclusion, high expression of topo IIα was predictive of worse survival, and high expression of topo IIβ was predictive of lower response rates. Furthermore, lower survival probability was observed in patients with bcl-2-positive tumors. Immunohistochemical assessment of these markers in diagnostic biopsies may give important prognostic information and may help selecting patients in the worse prognostic categories for new therapeutic strategies.