Long-term survival rates high for pediatric low-grade gliomas

Stuart H. Burri, MD

Bandopadhayay and colleagues performed a review of the SEER database for pediatric patients with low-grade glioma. An impressive 4,040 cases were identified over a long time period (1973-2008). There are a large number of patients, but with significant inhomogeneity of patients treated over such a large time span. As a SEER analysis, there is very limited specific detail as to how each patient was managed. It is important to realize that a significant portion of the patients were initially treated in the era prior to routine availability of MRI, which certainly had a revolutionary effect on both surgical treatments as well as the advent of progressively more sophisticated radiation planning techniques made possible with advancing imaging and computer technology.
Many of the findings are not surprising and parallel our current understanding. Patients with nonpilocytic tumors and those with higher grade had inferior survival, as did those diagnosed prior to 1989.  
The primary take-home — and potentially new — message is that, as patients reach adulthood, there are few deaths in the population of long-term surviving low-grade glioma patients. That is encouraging for all clinicians who treat these patients.
The authors are correct that one of the goals of therapy should be to minimize toxicity associated with therapy. They did find that, on multivariate analysis, there was an increased risk for death in children treated with radiation therapy.
It is important to note that this is a purely observational analysis, and that disease-specific factors play a huge role in the selection of therapy and subsequent outcome. The patients who received radiation generally would be in the higher risk group for all of the other significant factors, including histology (both nonpilocytic and grade II), diagnosis pre-1989, noncerebellar glioma and non-gross total resection, with the exception of patients aged less than 2 years at diagnosis.
Presumably, all patients with progressive disease ultimately would be treated with radiation therapy even if the initial goal is to manage with alternative approaches, such as chemotherapy. Less than 20% of patients in the analysis received radiation therapy, lending further credence to the theory that only the highest-risk patients, or those with progressive tumors, were treated. These high-risk patients also would be more likely to be exposed to other potentially harmful treatments, such as further surgery, or chemotherapy. The researchers in this study did not include chemotherapy in their analysis, presumably because the data are limited in the SEER database. As the researchers noted: “It is, however, important to acknowledge that it is difficult to determine from the SEER data how much of this is due to radiation itself and how much is a reflection of selection bias.”
Again, the authors should be congratulated for the large analysis and long-term follow-up showing the lack of late tumor progression and subsequent death. The conclusions regarding radiation therapy need to be significantly tempered by the unavoidable selection bias inherent in any SEER analysis.