OBJECTIVES: The purpose of this study was to evaluate the maximum cost-effective price (CEP) supported for innovative drugs co-administered with existing branded therapies. METHODS: An early economic model was constructed in Microsoft Excel using a three-state partitioned-survival approach. The intervention arm was assumed to be a hypothetical regimen consisting of an add-on drug and an anchor branded therapy, while the comparator consisted of the anchor therapy; both arms were dosed to progression. Three pricing scenarios were evaluated for the anchor: £1,000/month (low cost), £3,000/month (moderate cost), and £5,000/month (high cost). Other costs were sourced from a literature review; adverse event costs were not included. Progression-free survival (PFS) and overall survival (OS) were modelled assuming an exponential distribution; different median PFS and OS gains were evaluated to determine the maximum cost-effective price permitted for the add-on therapy. The maximum supported price was evaluated at two different willingness-to-pay (WTP) thresholds: £20,000/QALY and £50,000/QALY. All costs and outcomes were discounted at 3.5%. RESULTS: For small gains in OS and PFS (<3 months), the model projects that no CEP for the add-on would be supported at a WTP threshold of £20,000/QALY. When administered with a low-cost anchor, the add-on would be cost-effective at a WTP of £50,000/QALY with a price up to £583/month; when administered with a high-cost therapy, no CEP was supported. In order to support any CEP for the add-on, substantial gains in OS are required: for a PFS gain of 3 months, a gain of 6.9 months for OS would be required at a WTP of £50,000/QALY. CONCLUSIONS: These results demonstrate that new drugs co-administered with anchor branded therapies require substantial OS gains to support cost-effective pricing, as these drugs are dosed to progression. This analysis highlights the utility of early economic models in evaluating potential pricing and HTA barriers early in the development process.