[Epidemiology of cancer pain].

The prevalence of pain in cancer patients is influenced by several factors, for example the cancer disease, stage of disease, metastases present and treatment. However, only very few studies take all these factors in account when presenting the prevalence of pain in cancer patients. Pain may be caused by direct tumour infiltration, but may also be indirectly related to the cancer disease, caused by the cancer treatment or unrelated to the cancer. The most frequent pain quality is somatic pain followed by visceral and neuropathic pain. Pain with certain qualities or characteristics, such as incident pain, tenesmi in the gastrointestinal tract or cramps located to the bladder or rectum are more difficult to relieve than other pains. Other factors, such as major psychological distress, fast increasing doses of opioids and a past history of addictive behaviour may also be predictive of a poor treatment outcome. Besides pain cancer patients may also suffer from other troublesome symptoms such as asthenia, anorexia, constipation, nausea and vomiting and poor quality of sleep. These symptoms have great impact on the patients' well-being and should be treated contemporarily.