Measuring the quality of life of cancer patients: interpret the results with caution.

When evaluating the efficacy of cancer drugs, increase in overall survival is the gold standard outcome. The high burden of adverse effects associated with cancer treatments has led to an interest in measuring patients' quality of life. The most relevant quality of life rating scales are self-reported and assess at least three dimensions: physical, psychological and social. Some scales can be used in all patients and healthy subjects, while others are disease-specific. Some personalised scales exist, which take into account the factors that are most important to an individual patient. Some scales only evaluate adverse effects. Some scales that are frequently used in oncology only assess one dimension of quality of life. It is not easy for non-specialists to interpret quality of life scales. We suggest a few questions to help with interpreting the data.