A drug can have the best clinical profile in its class and still underperform for a reason that has nothing to do with medicine. The commercial team did not account for how long payers take to decide whether they will cover it. In oncology, where patients move through lines of therapy quickly and treatment windows are narrow, a delay in access of a few months can mean a permanently smaller market.
Stelios Tzellos of the UK has watched this happen across the industry. As a professional in business insights, analytics, and oncology marketing at AstraZeneca, with prior roles at GlobalData and IQVIA, he treats market access timing as a core forecasting input rather than a detail to be sorted out after launch.
Approval Is Not Access
Regulatory approval gives a company permission to sell a drug. It does not give patients a way to receive it. Between those two points sit payers, formularies, and reimbursement decisions that operate on their own timelines. A drug approved in January might not appear on a major formulary until well into the year, and in some markets the gap is longer.
Forecasting teams often model the approval date as the inflection point and assume revenue ramps from there. The real ramp starts when access clears, and access clears at different speeds in different places. A model that treats approval and access as the same event will front-load revenue that arrives later, if it arrives at all.
Why Oncology Punishes Delay
In many therapeutic areas, a patient who cannot start a drug this month starts it next month. The market simply shifts in time. Oncology does not forgive delay so easily. A patient progressing through treatment lines may move past the point where a given drug is appropriate. A patient may start a competitor’s therapy that was available first and stay on it. In the most serious cases, the patient may not have the time to wait.
This means a delay in access does not just postpone revenue. It can erase a portion of it permanently. Tzellos understands this from working on oncology disease insights at IQVIA, where the interaction between access timing and treatment sequencing showed up directly in how markets developed.
The Markets That Move at Different Speeds
Access timelines vary enormously across geographies. Some health systems make rapid coverage decisions. Others run lengthy assessments that weigh cost against clinical benefit before granting reimbursement. A forecast that applies one timeline across all markets will be wrong in most of them.
Tzellos worked with global pharmaceutical clients at IQVIA and now operates inside a company with one of the most active oncology portfolios in the world. Reading those differences correctly is the difference between a forecast that holds and one that unravels market by market.
Building Access Into the Forecast
The fix is to model access as its own variable, with its own timeline, in each major market. That means working with market access colleagues early rather than treating their input as a late-stage review. It means building scenarios around fast, average, and slow access outcomes. And it means tracking formulary decisions as they happen so the forecast updates with reality.
At GlobalData, Tzellos built epidemiology models and competitive assessments for oncology and haematology indications including Hodgkin’s lymphoma. At AstraZeneca, he leads cross-functional projects that bring market access into the planning conversation from the start. When access is part of the plan, the forecast describes the market that will actually be there.