Lean Body Mass as a Determinant of Docetaxel Pharmacokinetics and Toxicity

Docetaxel is used as a first line anti-cancer drug in the treatment of several cancers, mainly breast- and metastatic castration-resistant prostate carcinoma. Anti-cancer drugs are being dosed based on patients estimated Body Surface Area in order to equalize total drug exposure. Nevertheless, docetaxel treatment is characterized by highly interindividual pharmacokinetic variation leading to toxicity and under-treatment. For most anti-cancer drugs, including docetaxel, other anthropometric parameters, such as Lean Body Mass (LBM), have been suggested to be superior to Body Surface Are (BSA) as a determinant for dosing but this has not been implemented in clinical practice. The investigators will determine which anthropometric parameters, LBM, total body weight (TBW) or BSA correlate best to docetaxel exposure (AUC) for both males and females. The investigators will determine if occurrence of docetaxel toxicity can be related to dose/LBM. The investigators will determine which methods to measure LBM: DEXA, Bioelectrical Impedance Assessments (BIA) or formula estimates are accurate enough for dosing calculations to be used for dosing docetaxel.