Holding back the sea: the role for maintenance chemotherapy in metastatic breast cancer

Excerpt

While prolongation of overall survival (OS) is perhaps the central (implicit or explicit) goal of many oncologists and patients considering systemic therapies for metastatic breast cancer (MBC), in reality most studies do not demonstrate an OS benefit for one treatment regimen over another. Indeed, no studies have been performed to demonstrate a survival difference for an individual therapy versus best supportive care [1]. Studies that have bucked this trend are two studies with molecular-targeted therapies including the pivotal study of chemotherapy with or without trastuzumab [2], as well as the recently reported randomized phase II study of chemotherapy with or without the inhibitor of poly(ADP) ribose polymerase, BSI-201 [3] (although confirmatory phase III data is awaited). In addition, two studies of taxane/antimetabolite combination chemotherapy versus taxane monotherapy demonstrated an improvement in OS with the combination arm [4, 5]. However, neither study had a crossover design, with less than a quarter of patients randomized to taxane monotherapy in each study receiving the antimetabolite, leaving the question of how sequential treatment with the same agents would compare to the concurrent treatment unanswered. The only phase III study with a crossover design allowing comparison of concurrent with sequential therapy demonstrated no OS advantage with doublet therapy [6]. On the whole, in phase III MBC clinical trials, OS is rarely improved despite significant gains in other parameters such as response rate and progression-free survival (PFS). The commonly cited explanation for this observation is the “embarrassment of riches” in the breast cancer armamentarium; with many patients receiving multiple lines of active therapy over the course of their disease, a potential survival advantage related to one individual link in the chain may be diluted. Crossover to the more active treatment arm of clinical studies following unblinding at the time of interim analyses may also be a factor. Accordingly, measures of progression and/or response rather than OS have emerged as major clinical endpoints of most randomized clinical studies in advanced breast cancer. …