Post-Treatment FDG-Avid Splenic Lesions in DLBCL: Clinical and Radiographic Characteristics for Risk Assessment

PET-CT has been widely incorporated in the treatment of diffuse large B cell lymphoma (DLBCL) and Hodgkin's lymphoma (HD) both for staging at diagnosis and for evaluation of response to therapy. Residual FDG-avid lesions at the end of treatment (EOT) are often due to infectious or inflammatory process and not due to refractory lymphoma. Nonetheless, such lesions prompt diagnostic and therapeutic interventions. In the present study, we evaluate clinical and radiological characteristics of patients with EOT FDG-avid splenic lesions in hope to provide better tools to discern false from true lesions.

The study cohort included patients with DLBCL or HD who had residual EOT FDG-avid splenic lesion with no evidence of active disease in other sites. Patients were concluded as false positive or true positive according to pathological results or long-term follow-up. Clinical and PET-CT characteristics were compared between the two groups.

Our cohort included 9 patients with DLBCL and 2 with HD, of which 6 patients were determined to have false positive lesions and 5 true positive.

Comparing metabolic volume (MV) ratio between EOT to interim (EOT/interim) tests showed a marked difference between false positive and true positive lesions (0.5 vs 3.6, p= 0.02). Notably, comparing EOT to diagnosis (EOT/Dx) MV showed a similar trend that did not reach statistical significance, highlighting MV EOT/interim ratio as a parameter with higher discriminative ability. EOT SUVmax was also significantly different between false positive and true positive (7 vs. 19, p=0.02). A MV EOT/interim ratio >3 has a 75% sensitivity and 100% specificity for the true positive group. Other clinical and PET-CT characteristics were not found to statistically differ between the groups.

To date, this is the first report showing predictive ability of PET-CT characteristics to discern true from false positive residual FDG-avid splenic lesions. Our cohort is of small numbers, nonetheless, EOT/interim MV shows a clear opposite ratio with a decrease in the false positive compared to an increase in the true positive groups. We suggest EOT/interim MV ratio might be a tool to identify patients at low risk of refractory disease allowing non-invasive surveillance. Further larger studies will be needed to validate the role MV EOT/interim ratio as a tool to discriminate residual disease from false positive FDG-avid lesions.