Staging fdg‐avidity in extranodal marginal zone lymphoma (emzl) by disease location

Introduction: Fluorodeoxyglucose (FDG)-PET/CT is the standard imaging modality to assess initial tumor burden and response to therapy in lymphoma. FDG-avidity in EMZL remains unclear with variability by extranodal locations. Thus, the current Lugano staging suggested to use CT scans in EMZL. Recent data is challenging this suggestion. Thus, we evaluated FDG-avidity in EMZL using a large MZL database. Methods: We assessed the University of Miami MZL database searching for patients with staging PET/CT. Currently, this database includes 715 patients with 578 (80.8%) patients with EMZL; 152 (26.3%) have staging PET/CT and were analyzed. Patients with high-grade transformation at diagnosis were excluded. In patients with >1 extranodal site, each location was counted independently providing a total of 187 locations. PET/CTs were reviewed by expert radiologists to ascertain tumor and not surrounding tissue avidity, with specific attention to ocular and GI locations; if scans were not available (n = 15), we retrieved data from reports. GI involvement was defined as focal uptake above normal physiologic GI activity. We considered FDG-avid disease if SUVmax was ≥2 and calculated ratios between lymphoma SUVmax with mediastinal blood pool (BP index) and liver background (Liver index). Results: This cohort includes 152 patients (2/2016–1/2023) with EMZL. Most patients were women (n = 88, 58%), median age 62 years (range 33–83), and Hispanics (n = 77, 51%). LDH was largely normal (n = 126, 83%) with most patients having early-stage disease (n = 98, 64%). Among 187 EMZL locations, most common were gastric (n = 33,17.6%), ocular (n = 31, 16.6%), lung (n = 30, 16%), skin and soft tissue (n = 16, 8.6%, each), salivary gland (n = 13, 7%), airways (n = 11, 5.9%), and breast (n = 9, 4.8%). Most common FDG-avid locations (SUVmax ≥2) were salivary gland (100%), soft tissue (93.8%), lung (93.3%), ocular (93.5%, with conjunctiva FDG-avid in 75%), airways (90.9%), bone (83.3%), GI-nongastric (80%), gastric (72.7%), and breast (44.4%). Skin (93.8%) was a largely non-FDG avid location (Table 1). Median size of FDG-avid lesions was 2.4cm (range, 0.7–17.4). All 22 patients with multiple mucosal sites demonstrated FDG-avidity in at least one site, and 17 across all sites. In patients with data about background FDG avidity (n = 150), a BP index and Liver index ≥1 detected lymphoma in 79.3% and 71.5%, respectively. Both indexes failed to identify skin and breast EMZL (Figure 1A,B). The research was funded by: Sylvester Comprehensive Cancer Center National Cancer Institute (NCI) core grant P30CA240139 Keywords: extranodal non-Hodgkin lymphoma, indolent non-Hodgkin lymphoma, PET-CT No conflicts of interests pertinent to the abstract.