This study will evaluate the safety of the matrix fentanyl patch. The study will be conducted in opioid-tolerant patients with moderate to severe cancer pain currently taking an around-the-clock opioid. Patients will discontinue their current opioid regimen and begin using ZR-02-01 as soon as possible under the direction of the physician investigator upon entry into the study. Patient's dose of ZR-02-01 will be determined by the investigator using sponsor-provided conversion. Pain therapy will be under the supervision of the physician investigator.