A Phase II Trial of Carboplatin (CBDCA) in Small-Cell and Non-Small-Cell Lung Cancer with Correlation to In Vitro Analysis of Cytotoxicity

Abstract

A Phase II trial of carboplatin (CBDCA) was performed in 33 patients with advanced lung cancer, including 15 patients with inoperable Stage III non-small-cell (NSCLC) and 18 patients with relapsed small-cell (SCLC) lung cancer. Initial dosage was 320 mg/m2 infused over 24 h; in the absence of hematologic toxicity, subsequent doses were escalated to 400 mg/m2. Patients received a median of two cycles (range 1-13 for NSCLC and 1-5 for SCLC) of therapy. There were no complete or partial responses among the NSCLC patients. Among the SCLC patients, two had a partial response. In vitro analysis of the cytotoxicity of CBDCA and its parent compound cisplatin by two different methods for 20 NSCLC cell lines suggested that equivalent tumor cell kill is achieved by the two compounds, but this occurs at a log lower concentration of cisplatin than of CBDCA. The in vitro cytotoxicity against NSCLC of CBDCA at a concentration predicted to be in the range produced by the dose employed in this Phase II study correlated well with the resulting very modest in vivo benefit. In vitro, a continuous dose-response relationship exists for CBDCA, suggesting that if higher doses could be administered safely to patients, greater clinical benefit might occur. We conclude that single agent CBDCA in the dosage and schedule administered has less than 20% activity (95% confidence intervals 0-19%) in NSCLC and an 11% response rate in SCLC (95% confidence intervals 2-34%). Despite this outcome, in vitro data in human NSCLC cell lines suggest higher dosages should perhaps be evaluated before discounting a role for CBDCA in the management of NSCLC.