Background: Combination chemotherapy can cause greater tumour cell kill if the drug dose is not compromised, while sequential single agent chemotherapy may allow for greater dose intensity and treatment time, potentially meaning greater benefit from each single agent. In addition, sequentially using single agents might cause less toxicity and impairment of quality of life, but it is not known whether this might compromise survival time.
Objectives: To assess the effect of combination chemotherapy compared to the same drugs given sequentially in women with metastatic breast cancer.
Search methods: We searched the Cochrane Breast Cancer Group Specialised Register, using the search terms "advanced breast cancer" and "chemotherapy", MEDLINE and EMBASE on 31 October 2013. The World Health Organization International Clinical Trials Registry Platform and ClinicalTrials.gov were also searched (22 March 2012).
Selection criteria: Randomised controlled trials of combination chemotherapy compared to the same drugs used sequentially in women with metastatic breast cancer in the first-, second- or third-line setting.
Data collection and analysis: Two authors independently extracted data from published trials. Hazard ratios (HR) were derived from time-to-event outcomes where possible, and a fixed-effect model was used for meta-analysis. Response rates were analysed as dichotomous variables (risk ratios (RR)), and toxicity and quality of life data were extracted where available.
Main results: Twelve trials reporting on nine treatment comparisons (2317 patients randomised) were identified. The majority of trials (10 trials) had an unclear or high risk of bias. Time-to-event data were collected for nine trials for overall survival and eight trials for progression-free survival. All 12 trials reported results for tumour response. In the 12 trials there were 1023 deaths in 2317 women randomised. There was no difference in overall survival, with an overall HR of 1.04 (95% confidence interval (CI) 0.93 to 1.16; P = 0.45), and no significant heterogeneity. This result was consistent in the four subgroups analysed (risk of bias, line of chemotherapy, type of schema of chemotherapy, and relative dose intensity). In particular, there was no difference in survival according to the type of schema of chemotherapy, that is whether chemotherapy was given on disease progression or after a set number of cycles. In the eight trials that reported progression-free survival, 678 women progressed out of the 886 women randomised. The combination arm had a higher risk of progression than the sequential arm (HR 1.16; 95% CI 1.03 to 1.31; P = 0.01) with no significant heterogeneity. This result was consistent in all subgroups. Overall tumour response rates were higher in the combination arm (RR 1.13; 95% CI 1.03 to 1.24; P = 0.008) but there was significant heterogeneity for this outcome across the trials. In the seven trials that reported treatment-related deaths, there was no significant difference between the two arms, although the CIs were very wide due to the small number of events (RR 1.53; 95% CI 0.71 to 3.29; P = 0.28). The risk of febrile neutropenia was higher in the combination arm (RR 1.32; 95% CI 1.06 to 1.65; P = 0.01). There was no statistically significant difference in the risk of neutropenia, nausea and vomiting, or treatment-related deaths. Overall quality of life showed no difference between the two groups, but only three trials reported this outcome.
Authors' conclusions: Sequential single agent chemotherapy has a positive effect on progression-free survival, whereas combination chemotherapy has a higher response rate and a higher risk of febrile neutropenia in metastatic breast cancer. There is no difference in overall survival time between these treatment strategies, both overall and in the subgroups analysed. In particular, there was no difference in survival according to the schema of chemotherapy (giving chemotherapy on disease progression or after a set number of cycles) or according to the line of chemotherapy (first-line versus second- or third-line). Generally this review supports the recommendations by international guidelines to use sequential monotherapy unless there is rapid disease progression.