Colson, J., Koyyalagunta, D., Falco, F.J., & Manchikanti, L. (2011). A systematic review of observational studies on the effectiveness of opioid therapy for cancer pain. Pain Physician, 14(2), E85–E102. Retrieved from http://www.painphysicianjournal.com/2011/march/2011;14;E85-E102.pdf

To assess current literature regarding the overall effectiveness of opioid therapy in cancer pain management

• Databases searched were PubMed, EMBASE, the Cochrane Collaboration, and ClinicalTrials.gov for the period 1996–June 2010. Investigators also searched bibliographies manually.
• Authors did not supply search keywords.
• Studies were included in the review if they were observational studies involving adults older than 18 years old who were being treated with any opiod for cancer-related pain.
• Authors did not supply exclusion criteria.

• The initial search retrieved 1,916 references. Investigators identified 53 observational studies for review. Of those 53, investigators analyzed 18.
• Investigators assessed the quality and validity of studies by using the Agency for Healthcare Research and Quality (AHRQ) criteria for assessing the quality of observational studies. Investigators graded studies by using the five levels of evidence developed by the United States Preventive Services Task Force.

• Seven studies met the criteria for methodology quality by achieving an evidence synthesis score equal to or greater than 50 (out of a possible score of 100) in regard to AHRQ criteria.
• The range of sample sizes was 55–589, with a total number of samples across studies of 1,619.
• All subjects had at least moderate to severe pain.

Studies involved a variety of opioid types and varied in terms of duration of follow-up, as the summaries that follow show.

• Transdermal opioid-delivery systems: Two large studies showed that transdermal opioids were effective and well tolerated. Authors conclude that transdermal fentanyl-buprenorphine shows promise. 
• Sustained-release oral opioids: Different types of formulations are available, and authors state that evidence shows them to be effective and safe. However, the review included only one study of sustained-release oral opiods, and data from this study showed poorer results at the end point than at the baseline.
• Breakthrough pain: Two studies showed oral preparations of fentanyl to be effective and well tolerated.
• Multimodal analgesic therapy: In one study, an nonsterioidal anti-inflammatory drug (NSAID) was added to a continuous morphine infusion. The addition of the NSAID improved analgesia.
• Intrathecal opioid administration: In one study, as a last resort, patients received an opioid via intrathecal route. Results showed long-term improvement over four years or until death. This study had a low AHRQ score.

This review identified evidence of moderate strength, from observational studies, regarding the effectiveness of opioids as a treatment for cancer pain. Authors strongly recommend opioids, by various routes, for the management of cancer-related pain.

Authors note that further evidence is needed in the areas of dose response and treatment for breakthrough pain.

Opioids by various routes remain the mainstay of cancer-pain management. Some evidence suggests that the addition of an NSAID can improve results and that use of fentanyl formulated for rapid onset and short duration is effective and well tolerated for breakthrough pain. Additional research in breakthrough pain is needed.