Various Diagnostic Criteria by PET/CT May Assist in Predicting Richter Syndrome in CLL

A recent study published in Clinical Lymphoma, Myeloma, & Leukemia suggests a potential role for a noninvasive diagnostic tool to stratify patients with chronic lymphocytic leukemia (CLL) who are at risk of developing Richter syndrome (RS) by examining semiquantitative PET/CT imaging parameters.

PET/CT imaging that utilized the radiotracer 2-deoxy-2-[18F]fluoro-D-glucose (2-[18F]-FDG) was qualitatively and semiquantitatively studied and compared with clinical/histological variables in 80 patients with CLL. Kaplan-Meier overall survival (OS) curves were also observed to detect differences between groups stratified by diagnostic features.

“Our results confirmed the accuracy of PET/CT parameters in discriminating patients with risk to RS,” wrote the study authors. “The detection of patients [who] will develop RS is crucial because RS affects significantly survival and common biological and clinical features have some limitations in this field.”

Of the total cohort, 78 (97.5%) patients were FDG-avid and showed higher 2-[18F]-FDG uptake at the biopsied lesions, which was an enlarged lymph node the majority of cases. PET/CT results were compared with histological findings from the lymph node or extranodal biopsies performed within 21 days from PET/CT study.

PET/CT metabolic parameters that were significantly associated with RS were maximum standardized uptake value body weight (SUVbw), lean body mass (SUVlbm), body surface area (SUVbsa), lesion-to-blood SUV ratio (L-BP SUV R), and lesion-to-liver SUV ratio (L-L SUV R). Investigators were able to identify thresholds which were indicative of a higher risk of RS using these diagnostic criteria, confirming the accuracy of PET/CT for predicting its development.

As an example, the investigators used SUVbw to demonstrate the utility of determined cutoff values for predicting RS. In their analysis, the investigators settled on an SUXmax value of 9 as the best compromise between sensitivity (67%) and specificity (90%) for predicting RS by SUVbw. The resulted supported this conclusion, with RS occurring in 12 of 18 patients with high SUVmax (>9) versus only 6 out of 68 patients with low or moderate FDG uptake.

Overall, median OS was significantly shorter in patient with RS at 15.6 months versus 27.8 months in those without (P = .001). By univariate analysis, Binet stage, the presence of B symptoms, RS phenomenon, prior therapy, SUVbw, SUVbsa, SUVlbm, L-BP SUV R, and L-L SUV R were all significantly associated with OS.

Variables of total lesion glycolysis and metabolic tumor volume as well as most clinical/histological parameters were not correlated with RS occurrence or OS.

The investigators endorsed the importance of their findings as being the first study of its kind to examine metabolic parameters other than SUVbw for predicting RS. This is important since SUVbw is limited by many variables such as time between injection and scan, lesion size, risk of extravasation of the radiotracer, decay of the radiotracer, and residual activity of the syringe among others. The results suggest that PET/CT imaging could be used to better define a patient’s pathological condition, in turn leading to more personalized approaches.

The retrospective study design and the relatively low sample size of the population are limitations acknowledged by the investigators and further studies with larger cohorts would be necessary to clarify the role of PET/CT in this setting.

Reference:

Albano D, Camoni L, Rodella C, Giubbini R, Bertagna F. 2-[18F]-FDG PET/CT role in detecting richter transformation of chronic lymphocytic leukemia and predicting overall survival. Clin Lymphoma Myeloma Leuk. Published December 9, 2020. doi: 10.1016/j.clml.2020.12.003