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.