Stelios Tzellos | Why Oncology Commercial Teams Still Misunderstand Real-World Evidence

Stelios Tzellos

Clinical trial data tells pharmaceutical companies how a drug performed under controlled conditions. Real-world evidence tells them what happens when that drug enters the messiness of actual clinical practice. The problem is that most commercial teams still treat real-world evidence as a post-launch marketing tool instead of what it really is: one of the most important strategic inputs in oncology.

Stelios Tzellos of the UK has spent years working across oncology analytics, forecasting, and commercial strategy, and one pattern continues to repeat itself across the industry. Companies build launch plans around clinical trial assumptions and only later discover that physician behaviour, patient adherence, and treatment sequencing in the real world look very different.

The Gap Between Clinical Trials and Clinical Practice

Randomized clinical trials are designed to isolate variables. They exclude certain patient populations, tightly control treatment protocols, and measure outcomes under highly structured conditions. That rigor is necessary for regulatory approval, but it also means the trial environment often looks nothing like community oncology practice.

A commercial forecast built entirely on trial assumptions can therefore miss key adoption barriers. Physicians may hesitate to prescribe a therapy to older or more complex patients who were excluded from the study population. Biomarker testing rates may lag behind expectations. Side effect management may prove more difficult outside specialist centres.

Tzellos encountered these challenges repeatedly during his work at GlobalData and IQVIA, where oncology forecasting projects increasingly depended on understanding how physicians behaved after launch rather than simply what the trial data suggested should happen.

Why Real-World Evidence Matters Earlier Than Pharma Thinks

Most pharmaceutical organizations still treat real-world evidence generation as something that happens after launch to support payer discussions or publication strategy. The smarter companies use it much earlier.

At AstraZeneca, where Stelios Tzellos works across business insights, analytics, and oncology marketing, real-world evidence increasingly informs forecasting assumptions, treatment sequencing models, and competitive positioning discussions before launch planning is finalized.

That’s because oncology markets move too quickly for companies to rely only on clinical trial readouts. Physicians adjust prescribing patterns based on conference discussions, peer experience, and observational outcomes long before formal guideline updates occur.

The Competitive Implications

Real-world evidence has also become a competitive weapon. In crowded oncology categories, multiple drugs may demonstrate similar efficacy in controlled trials. The differentiator becomes how those therapies perform in routine practice.

Commercial teams that understand this dynamic can position products more effectively. Teams that ignore it risk discovering too late that the market values convenience, tolerability, or treatment sequencing flexibility more than a statistically significant endpoint difference.

Building Better Commercial Strategy

Stelios Tzellos built his career at the intersection of scientific evidence and commercial strategy. His academic background in Molecular Biology at Imperial College London gave him the ability to evaluate evidence critically. His consulting experience at GlobalData and IQVIA taught him how to translate that evidence into forecasting and market planning. And his work at AstraZeneca requires applying those lessons to real commercial decisions.

The pharmaceutical companies that succeed in oncology over the next decade will not be the ones that simply generate more clinical data. They will be the ones that understand how evidence changes once it leaves the clinical trial environment and enters actual clinical practice.