Efficacy and Safety of Sublingual Fentanyl Tablets in Treatment of Breakthrough Pain in Cancer Patients.

Inclusion Criteria: * Males or females 17 years of age or older * Stable cancer-related pain. * Are receiving a stable, fixed-schedule oral opioid regimen equivalent to 60 to 1000 mg of oral morphine per day or transdermal fentanyl therapy equivalent to 50 to 300 µg/h, and are on a stable dose of opioid medication for relief of breakthrough pain for at least 14 days prior to screening. * Experiencing 1-4 episodes of breakthrough pain per day. * Meet the criteria defined in the Eastern Cooperative Oncology Group (ECOG) Performance Status for Grade 0, 1, or 2. Exclusion Criteria: * Are pregnant or lactating. * Have uncontrolled or rapidly escalating pain. * Have moderate to severe ulcerative mucositis. * Have a cardiopulmonary disease that would increase the risk of administering potent opioids. * Have neurologic or psychologic disease that would compromise data collection * Have any clinically significant condition that would, in the investigator's opinion, preclude study participation. * Are currently taking monoamine oxidase inhibitors (MAOIs), or have taken MAOIs within 14 days prior to enrolling in the study. * Have received strontium 89 therapy within 60 days prior to entering the study. * Have received anti-neoplastic therapy within 2 weeks of study entry that, in the investigator's opinion, will influence assessment of breakthrough pain * Have received any investigational drug (non-approved) within 30 days prior to the first dose of study medication, or are scheduled to receive an investigational drug other than EN3267 during the course of the study. * Have hypersensitivities, allergies, or contraindications to fentanyl. * Have a significant prior history of substance abuse or alcohol abuse. * May have difficulty complying with the protocol, as assessed by the investigator.