Improved anti-tumor response rate with decreased cardiotoxicity of non-pegylated liposomal doxorubicin compared with conventional doxorubicin in first-line treatment of metastatic breast cancer in patients who had received prior adjuvant doxorubicin: results of a retrospective analysis

Our objectives were to ascertain the safety (cardiotoxicity) and efficacy of non-pegylated liposomal doxorubicin Myocet (M) compared with conventional doxorubicin (A) in patients with metastatic breast cancer (MBC) who had received adjuvant anthracycline treatment and were at high risk of developing iatrogenic cardiomyopathy. This retrospective analysis is based on data pooled from two prospective phase III comparative randomized clinical trials comparing Myocet versus conventional doxorubicin in combination with cyclophosphamide and as single agents, respectively, for the treatment of MBC. The outcome measures reviewed in this analysis were overall response, time to treatment failure, time to disease progression, overall survival and cardiotoxicity. The analysis was carried out by strata according to patients' previous exposure to adjuvant anthracyclines. Kaplan-Meier, log-rank chi-test, Cox proportional-hazards and Cochran-Mantel-Haenszel statistics were used for the analysis. Sixty-eight patients were included in this analysis: 29 and 39 patients from Studies 1 and 2, respectively, had received adjuvant anthracycline treatment. Study 1, with n=297, compared M 60 mg/m (M60) plus cyclophosphamide (C) 600 mg/m (C600) versus A 60 mg/m (A60) plus C600 as first-line treatment for MBC. Twenty-nine patients had received prior adjuvant doxorubicin, of whom, after randomization, 14 received M60+C600 and 15 received A60+C600 for the treatment of MBC. Study 2, with n=224, compared M 75 mg/m (M75) with A 75 mg/m (A75) as first-line treatment for MBC disease. Thirty-nine patients had received prior adjuvant doxorubicin, of whom, after randomization, 18 received M75 and 21 received A75 for their MBC. Hence, 32 patients received M-containing regimens and 36 received A-containing regimens for the treatment of MBC. Median age in both groups was 54 years. The groups were well balanced in terms of demographic characteristics. Overall response rates were 31% and 11% for M-treated patients and A-treated patients, respectively (Cochran-Mantel-Haenszel P=0.04, odds ratio=4.0). Median time to progression was 4.5 versus 3.4 months log-rank P=0.66, hazard ratio (HR)=1.14, median time to treatment failure was 4.2 versus 2.1 months (log-rank P=0.01, HR=2.06) and median survival time was 16 versus 15 months (log-rank P=0.71, HR=1.12). Cardiac events occurred in 22% of M-treated patients one congestive heart failure (CHF) versus 39% of A-treated patients (three CHFs) (log-rank, P=0.001). Median lifetime dose at onset of cardiotoxicity was 780 mg/m for M versus 580 mg/m for A (log-rank P=0.001, HR=4.8). This retrospective analysis shows that treatment based on non-pegylated liposomal doxorubicin (Myocet) significantly reduced the risk of cardiotoxicity in patients with MBC who had received prior adjuvant doxorubicin. Furthermore, anti-tumor activity and time to treatment failure were significantly improved compared with patients who received treatment based on conventional doxorubicin for their MBC. This analysis revisits the therapeutic option of including doxorubicin in the treatment of MBC patients who have had prior adjuvant anthracycline exposure.