Background: For patients with cancer, uncontrolled pain can reduce quality of life, lead to treatment breaks, and result in worse cancer outcomes. Guideline-concordant treatment for chronic, severe pain can include long-acting opioid formulations. Pain medications, however, often face prior authorization (PA), which requires providers to obtain payor pre-approval and may result in delayed or denied care. This analysis characterizes PA-related denials for pain medications for patients with cancer. Methods: At an urban comprehensive cancer center, we identified all PA requests for outpatient long-acting opioid (i.e., buprenorphine, fentanyl, hydromorphone, methadone, morphine, oxycodone, oxymorphone, tapentadol) prescriptions from 2023 and described frequency of PA approvals and denials. For denials, chart review 2 weeks post-PA was conducted of provider notes and patient communications with results summarized qualitatively. Results: 1752 new long-acting opioids prescriptions for 982 unique patients required PA. Of those, 1567 (89.4%) were approved after PA process, 99 (5.6%) were denied, 81 (4.6%) were cancelled after PA initiation, and 6 (0.3%) were unresolved. Most were prescribed by pain specialists including supportive care (n = 699, 40.0%) and anesthesia/pain medicine (n = 444, 25.3%) with most common indication: “Neoplasm related pain (chronic)” (61.1%). Oxycodone was the most common long-acting opioid requiring PA (n = 551, 31.4% of prescriptions), followed by fentanyl (n = 501, 28.6%), hydromorphone (n = 205, 11.7%), and methadone (n = 137, 7.8%). Long-acting morphine was denied most frequently (16.3% of n = 129 PA requests denied), followed by buprenorphine (12.1% of n = 33), and hydromorphone (7.3%). Fentanyl was denied the least (2.8%). The 99 denials affected 62 unique patients, including a patient with 7 denials. Chart review (n = 62) of the 2 weeks post-denial revealed a median of 2 (range 0-8) provider notes mentioning pain or PA barriers and median of 1 (range 0-5) patient calls or messages about the same. 22.6% (n = 14) patients ended up in the ER or admitted to the hospital for pain crisis or failure to thrive. Providers documented poor pain control, weight loss, need to “try and fail” other medications, and noted 11.3% (n = 7) patients ending up paying out of pocket for their medications. Patient messages document uncontrolled pain and unmanageable side effects with some literally begging for relief; one patient spoke of their fear of “dying in pain”. Conclusions: The vast majority of PA requests for long-acting pain medication result in approvals, suggesting that the process -which can delay essential pain management- is largely unnecessary. For the 1 in 20 requests that were denied, provider and patient concerns highlight the negative impact of uncontrolled pain. An improved, transparent PA process is essential for adequately treating chronic, cancer-related pain.