Study With Modafinil in Patients Treated With Docetaxel-Based Chemotherapy for Metastatic Breast or Prostate Cancer (MOTIF)

The primary objective is: * To determine the efficacy of modafinil in the reduction of fatigue in patients with metastatic breast or prostate cancer undergoing docetaxel-based chemotherapy The secondary objectives are: * To determine the effect of modafinil on quality of life (QoL) during docetaxel-based chemotherapy * To determine the effect of modafinil on patients physical activity level, functional status, number of chemotherapy cycles tolerated, sleep disturbance and depression, during docetaxel-based chemotherapy * To investigate the impact of tumour type, patient physical activity level, functional status, sleep disturbance and depression on the efficacy of modafinil at improving fatigue and quality of life during docetaxel-based chemotherapy. * To determine the safety and tolerability of modafinil during docetaxel-based chemotherapy