OBJECTIVES: As costs of healthcare continue to rise, payers need to quantify the potential patient population for a new treatment. In the case of a novel treatment for intractable pain that would be for end of life cancer patients, it was necessary to consider alternative methods for calculating the potential patient population size.  This study determined different approaches for identifying patient subpopulations in cancer for ‘end-of-life’ pain therapies   METHODS: PAREXEL conducted a literature search on the number of cancer pain patients with intractable pain.  Data was found on cancer patients with pain but not those at the end of their lives with intractable pain.  Alternative measures were considered, and cancer mortality data was identified as a surrogate for end of life cancer patients. The WHO’s guidelines on cancer pain estimate that 10 to 25% of cancer pain patients have intractable pain. Based on such surrogate measures, we were able to determine an estimated number of cancer patients with intractable pain at the end of their lives.  RESULTS: Prior to this study, the target patient population was estimated to be 156,000 in the US and an equivalent number in Germany, UK, Spain and France.  However, based on the surrogate measures, the results were much lower:  30,000 in the US and 31,000 in the 4 EU countries.  These numbers were validated by interviewing 22 pain clinicians in the US and EU and 23 payers in the US and EU.  CONCLUSIONS: By providing payers with accurate estimates of potential patient populations they will be better able to determine the cost implications of covering novel treatments. Given that the care provided to patients at the end of their lives is usually significantly higher than at any other time, treatments for end of life care have economic implications for payers.