Defining an Exposure Target for Weekly Paclitaxel Infusion in Breast Cancer Patients

Paclitaxel is a chemotherapeutic agent commonly used in various tumor types. Paclitaxel efficacy and toxicity are "dose-dependent" meaning that increasing the dose increases treatment efficacy and occurrence of toxicity. When used in the weekly 1-hour infusion regimen paclitaxel is commonly associated with treatment-limiting sensory peripheral neuropathy. At the current standard dose of 80 mg/m2 approximately 20-25% of patients experience treatment-limiting neuropathy. Drug exposure, not dose, determines treatment efficacy and neuropathy development. When treated with standard doses there is substantial variability in drug exposure meaning some patients are receiving less efficacious treatment than optimal. At this time we do not monitor a patient's exposure because the optimal exposure level has not been defined. The purpose of this study is to prospectively enroll patients for systematic collection of exposure and neuropathy data in order to characterize this relationship. Once the relationship between cumulative exposure and neuropathy has been characterized, this model will be used to define an exposure target in future prospective exposure-guided dose-adjustment trials.