Clinical trials to study pain in patients with advanced cancer: practical difficulties

Cancer is a common cause of death in our society and associated pain is prevalent in cancer patients. Despite this, pain is often not treated optimally. Although education (patient and caregiver) might improve the situation, many difficulties remain in carrying out clinical trials of new drugs or therapies in this particular group of patients. Appropriate controlled clinical trials need to be designed to maximise validity (randomised, blinding, quality of collected data, enough evaluable patients, statistical analyses) and effectiveness. Patient numbers are often small, the diseases and mechanisms of pain non-homogenous, and assessment techniques and analgesic requirements (and tolerance) may be variable. Furthermore, pain may be unstable, polypharmacy is often involved, behavioral and other cognitive factors may change, patient compliance may be suspect, and side effect profiles may be difficult to interpret (disease, patient status, polypharmacy). Strategies that may increase validity constrain the feasibility of the study and the generalisability of the study results obtained.