Patients with cancer often do not have an accurate perception of their prognosis and the risks and side effects associated with potential treatments. Research has highlighted several reasons for these information gaps. Where more than one medically acceptable treatment is available, doctors may have a strong preference for a particular treatment option and steer the treatment decision by skewed information disclosure. Also, fear of the nocebo effect may prevent the provision of balanced information on side effects. Knowledge of prognosis is essential for making well-informed treatment decisions, but doctors may be reluctant to discuss limited life expectancy with their patients because they fear loss of hope and the deterioration of the doctor-patient relationship. Communication on these difficult subjects should be better integrated into medical training.