Maximum Standard Uptake Value (SUVmax) on FDG-PET Imaging Predicts Time to First Treatment in Patients with Low Grade Follicular Lymphoma,

Most patients with asymptomatic advanced-stage low grade follicular lymphoma (FL) are managed by a ”watch and wait” strategy until they develop disease related symptoms or significant progression in tumor volume. The median time to first treatment (TFT) has been reported to be about 30 months from initial diagnosis (Ardeshna et al., Lancet 2003; 362: 516–22). Various prognostic factors such as FLIPI have been developed to estimate progression free survival and overall survival, but predictors for TFT from diagnosis have not been well defined in this population. The optimal frequency of follow-up and surveillance imaging remains unclear.

We reviewed our institutional database of FL patients who underwent [18F]-fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT) or FDG-PET imaging at diagnosis or as part of follow-up imaging during the ”watch and wait” period. Only patients with FL with low grade histologies (grade 1 or 2) on tissue biopsy who were untreated prior to FDG-PET imaging and with a minimum of 6 months of follow-up after the imaging were included in the analysis. SUVmax was defined as the highest lesional SUV on each scan and was determined by a nuclear medicine physician. ROC curve analysis was used to identify SUVmax cutoff values which would best predict short (≤ 6 months) vs. long (> 6 months) TFT with clinically relevant sensitivity and specificity for a training set of patients. The SUVmax cutoff value was then tested in another set of patients for the ability to categorize patients by TFT ≤ 6 months vs. > 6 months from imaging. Comparison between the two groups was performed using the Fisher's exact test. STATA 10.1 software was utilized for data analysis.

78 FL patients followed in our institution from 2001 until 2011 were included in the study. In the training set of 27 patients (median age 52 years, range 19–67), the ROC curve analysis revealed that an SUVmax cutoff at 10 could distinguish between those with TFT ≤ 6 months vs. > 6 months. When applied to the test set of 51 patients (median age 53, range 18–82), an SUVmax ≥ 10 was able to predict short TFT correctly in 14 out of 16 patients who required treatment ≤ 6 months from the FDG-PET or FDG-PET/CT scan (positive predictive value of 88%). SUVmax ≥ 10 had a high specificity in the test set (90%), but limited sensitivity (47%). A Fisher's exact test (two sided) confirmed that the association between SUVmax ≥ 10 and short vs. long TFT groups was statistically significant (p=0.006).

SUVmax ≥ 10 on FDG-PET or FDG-PET/CT imaging in patients with low grade FL can be used to identify those who will have a short TFT. An SUVmax cutoff at 10 could be an important factor in determining the frequency of clinical and imaging follow-up in asymptomatic, advanced-stage low grade FL patients who are managed by a ”watch and wait” strategy.

No relevant conflicts of interest to declare.