Measuring total metabolic tumor volume may improve the accuracy of prognosis prediction in follicular lymphoma patients, according to a study analyzing data from several clinical trials. But experts caution that the method still has too many uncertainties to be a valuable predictive tool.
The study, “Baseline Metabolic Tumor Volume Predicts Outcome in High–Tumor-Burden Follicular Lymphoma: A Pooled Analysis of Three Multicenter Studies,” was published in the Journal of Clinical Oncology.
Despite advances in lymphoma immunotherapy, about 20 percent of patients progress within two years of immunochemotherapy, showing a five-year overall survival of only 50 percent. Researchers at University Paris-Est Créteil in France noted that current models used to identify patients at high risk of progression and early death are not effective enough.
Working with colleagues at the University of Sydney in Australia, they explored whether total metabolic tumor volume could be a better option. This is acquired from positron emission tomography (PET) and computed tomography (CT) scans that measure the total burden of viable tumor and environmental cells.
The research team analyzed published data from three lymphoma clinical trials, where they identified 185 patients who had undergone the scans before treatment. Most patients, 92 percent, had stage 3-4 of the disease.
Prognosis had been estimated with the Follicular Lymphoma International Prognostic Index (FLIPI) and FLIPI2, and 37 percent of patients had a FLIPI score of 3 to 5, while 31 percent had a similar FLIPI2 score.
Patients were followed for a median of 64 months. Progression-free survival at five years was 55 percent, and overall survival was 92 percent. The median total metabolic tumor volume was 297 cm³, and the research team found that above a cut-off value of 510 cm³, patients tended to do much worse.
Indeed, among the 53 patients who had a total metabolic tumor volume of more than 510 cm³, the five-year progression-free survival was 33 percent and the overall survival was 85 percent. This was much lower than survival in patients with lower total metabolic tumor volumes; 65 percent and 95 percent for progression-free and overall survival, respectively.
An analysis showed that both the FLIPI2 score and the total metabolic tumor volume individually predicted progression-free survival. Based on the data, researchers could identify three risk groups.
Individuals with both a high total metabolic tumor volume and a FLIPI2 score of 3 to 5 had a five-year progression-free survival of only 20 percent. Having either a high metabolic tumor volume or a FLIPI2 score of 3 to 5 gave patients a five-year progression-free survival of 46 percent. Patients with neither high metabolic tumor volume nor high FLIPI2 scores had a progression-free survival of 69 percent.
In a linked editorial published in the same journal, researchers from Memorial Sloan Kettering Cancer Center in New York, however, argued that there are far too many uncertainties surrounding the study to conclude that total metabolic tumor volume is a good predictive measure.
They pointed out that the study was retrospective, and so measurements were done using different equipment and software, and patients were treated with different types of drugs. Such a lack of standardization makes data difficult to interpret, they argued.
If, however, future studies confirm that the method is a valuable tool, they said it is crucial to understand how metabolic tumor volume impacts survival in order to better use the data. Research needs to answer questions such as whether a higher volume indicates that a particular drug will be ineffective, or if patients with a higher volume need more treatment, or simply a more aggressive treatment.
Nevertheless, they believe the study is a first step in the right direction in the process of proving the method to be a valuable clinical tool.