Robert Louis, Neurosurgeon, Director of the Skull Base and Pituitary Tumor Program at Hoag Hospital, shared a post on LinkedIn:
“GBM Series | Post 3: The Metrics Illusion
Extent of resection has become the organizing metric of glioblastoma surgery.
The literature supports it. Greater resection correlates with longer survival. The data is consistent enough that the field has built an entire infrastructure around it – better imaging to define margins, better navigation to reach them, better intraoperative tools to confirm them. The logic is clean. Remove more tumor. Improve the outcome.
I use that logic in every case. I pursue maximum safe resection. I am not here to argue against it.
I am here to ask what happens when a single metric begins carrying more weight than it should.
Extent of resection is a surrogate endpoint. It measures what the surgeon did. It does not measure what the disease does next. And the distance between those two things in GBM is enormous.
A gross total resection confirmed on postoperative imaging is a surgical achievement. It is not a prognosis. The tumor’s molecular profile, its microenvironment, its response to adjuvant therapy – these determine trajectory far more than the completeness of what I removed. Every neurosurgeon who treats this disease knows this.
But the metric creates a gravity that is hard to escape.
When extent of resection becomes the primary measure of surgical success, the tools get optimized for it. The training gets organized around it. The conference presentations highlight it. The technology companies build products to maximize it. A feedback loop forms – and inside that loop, it becomes easy to mistake the metric for the outcome.
This is not unique to neurosurgery. Every field that adopts a measurable proxy eventually faces the moment when the proxy starts shaping behavior more than the underlying goal. The metric becomes the mission.
The danger is subtle. No one is claiming that extent of resection equals cure. But the culture – the way we present cases, the way we evaluate performance, the way we justify technology investments – quietly treats it as closer to the outcome than it actually is.
What gets lost in that gap is a harder conversation about what surgical success in GBM really means.
If I achieve gross total resection and my patient recurs in eight months, was the surgery successful? By the metric, yes. By the patient’s experience, the question is more complicated. If I leave a small residual to protect eloquent cortex and my patient preserves speech and function through their remaining time, the metric says I fell short. The patient may not agree.
I am not arguing that we abandon extent of resection. It matters. It should be pursued. But it should be held as what it is – one variable in a disease governed by many – rather than elevated into the singular benchmark of whether the surgeon did the job.
The field needs the discipline to measure what matters without confusing what we can measure with what matters most.
In GBM, those are not the same thing.”
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