This is an open label, long-term study carrying in multi-centers. Around 200 patients with moderate to severe cancer pain (NRS ≥ 4) who agreed and signed informed consent will be enrolled to receive oxycodone with continuous around-the-clock pattern. The study is to evaluate the safety and tolerability of cancer patients who receive CR and/or IR oxycodone. The number and percentage of patients with adverse events and serious adverse events will be recorded throughout the study.