Perioperative and longitudinal plasma GFAP in IDH-wildtype glioblastoma: a surrogate of extent of resection and a preoperative prognostic marker

Brain tumors are among the most formidable challenges in modern medicine, particularly a type called glioblastoma. This aggressive disease, which arises from the star-shaped support cells of the brain, grows rapidly and is notoriously difficult to treat. Even when surgeons remove as much of the visible tumor as safely possible and follow up with radiation and chemotherapy, the outlook remains grim for most patients. The amount of tumor left behind after surgery is a critical factor; removing more of it generally leads to longer survival. However, determining exactly how much was removed is not always straightforward. Surgeons rely on magnetic resonance imaging scans taken shortly after the operation, but these images can be clouded by blood from the surgery or obscured by the complex anatomy of the brain, making it hard to see if any cancer remains. Furthermore, during the long months of follow-up, it is often impossible to tell from a scan alone whether a new spot on the brain is a returning tumor or simply a reaction to the treatment itself. Because taking a new tissue sample from the brain is too risky to do routinely, doctors have long searched for a simpler way to monitor the disease, ideally through a blood test that could reveal what is happening inside the skull without the need for invasive procedures.

A team of researchers in Normandy, France, recently explored whether a specific protein found in the blood could serve as this missing link. They focused on a molecule called glial fibrillary acidic protein, or GFAP. This protein is a structural component of the star-shaped cells that make up the brain, and it is produced in large quantities by the cells that form glioblastomas. When these cells are damaged or broken apart, whether by the disease itself or by the physical act of surgery, GFAP leaks into the bloodstream. The researchers set out to track this protein in patients with a specific form of glioblastoma, known as IDH-wildtype, which is the most common and aggressive variant. They wanted to see if measuring GFAP at different times could tell them how much tumor was successfully removed, predict how long a patient might live, and help distinguish between a stable condition and a returning disease.

The study followed thirty-six adults who had just been diagnosed with this type of brain tumor. The researchers collected blood samples at four specific moments: just before the surgery, a few days after the operation when the body was still reacting to the trauma, and then again at three and six months during routine follow-up visits. They compared these blood levels with the results of the postoperative brain scans to see if the numbers matched what the images showed. The findings revealed a clear pattern in the days immediately following surgery. In nearly every patient, the level of GFAP in the blood jumped sharply within three or four days of the operation, rising from a median of 74 picograms per milliliter before surgery to 344 picograms per milliliter shortly after. This spike was expected, as the surgery itself causes some cell damage. However, the height of this spike told a different story depending on the success of the operation. Patients who had a complete removal of the tumor, where no visible cancer remained on the scan, saw their GFAP levels settle back down to very low numbers within three months. In contrast, patients who had a partial removal, leaving some tumor behind, maintained significantly higher levels of GFAP in their blood during that same period. The researchers found that a low level of GFAP a few days after surgery was a strong indicator that the surgeon had removed the entire tumor, while a high level suggested that some cancerous tissue remained.

Beyond just measuring the success of the surgery, the study showed that the amount of GFAP in the blood before the operation even began held important clues about the future. Patients who started with higher levels of this protein before their surgery tended to have shorter survival times. This was true regardless of how much tumor the surgeon managed to remove. Even among those who had a complete resection, those who began with high preoperative GFAP levels did not live as long as those who started with lower levels. This suggests that the protein is capturing something about the underlying nature of the disease, perhaps the total volume of the tumor or the extent of tissue damage, that exists before the surgeon ever makes an incision. The protein levels did not seem to be influenced by the patient's age, their general health, or specific genetic markers often used to classify these tumors, making it a standalone indicator of the disease's burden.

Perhaps the most surprising discovery concerned how the protein behaved when the disease returned. Many had hoped that a rising level of GFAP during follow-up would signal a new tumor growing back. However, the data showed that this was not the case. When patients developed a recurrence, their GFAP levels did not rise in a way that distinguished them from those whose disease was stable. Instead, the protein levels remained detectable only in those who had been left with a significant amount of tumor after their initial surgery. For patients who had a complete removal, the protein levels stayed low and undetectable, even if the disease eventually returned. This indicates that the test is not sensitive enough to catch a small, new tumor forming on its own, but it is very good at monitoring the presence of a larger, residual mass that was left behind. The protein acts less like a smoke alarm for a new fire and more like a gauge showing how much fuel is still sitting in the tank.

The researchers concluded that measuring GFAP in the blood offers a practical, non-invasive way to assess the success of brain tumor surgery and to gauge the remaining disease burden. While it cannot yet replace the need for brain scans or predict a recurrence on its own, it provides a valuable piece of the puzzle. A low level of GFAP shortly after surgery gives strong reassurance that the tumor was fully removed, while a high level warns that some cancer remains and requires closer attention. Similarly, a high level before surgery signals a more aggressive disease course, independent of the surgical outcome. This approach offers a simple, quantitative tool that could help doctors make better decisions about patient care, particularly in cases where imaging is difficult to interpret or when the goal is to monitor patients who still have tumor tissue remaining after their operation.