PET/CT in the Staging and Treatment Response Assessment of Patients With Extranodal Marginal Zone Lymphoma

¹⁸Fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) is the standard imaging modality in lymphoma. The 2014 Lugano classification considers extranodal marginal zone lymphoma (EMZL) a non-FDG-avid disease, recommending contrast-enhanced CT. We reassessed the utility of PET/CT for staging workup and response assessment of EMZL. We reviewed staging and response PET/CT of 190 EMZL sites from 152 patients. Each location was counted independently for patients with > 1 extranodal site. Although not standard, we considered FDG-avid disease if SUVmax was ≥ 2, and calculated ratios between lymphoma SUVmax and mediastinal blood pool (BP index) and liver background (liver index). FDG avidity was detected in 151 (79.5%) out of 190 extranodal sites (in 117 [76.7%] out of 152 patients), with a median SUVmax of 4.5 (IQR 2.5-6.9, range 0-26.8). Locations showing FDG avidity in > 90% of extranodal sites included salivary gland, bone, lung, soft tissue, ocular adnexa, and airways. Skin was commonly non-FDG avid (93.8%). Among 22 patients with > 1 extranodal location, there was concordant FDG avidity in all sites in 18 (81.8%) patients. Considering measurable extranodal disease size > 0.5 cm, we observed significant Pearson correlation coefficients (r) between lymphoma size and SUVmax (r = 0.20, p = 0.019, n = 142), BP index (r = 0.34, p < 0.001, n = 124), and liver index (r = 0.36, p < 0.001, n = 124). We also observed improved precision in response to treatment assessment in FDG-avid EMZL tumors. This study demonstrates that EMZL is commonly an FDG-avid disease, suggesting that PET/CT should be routinely used in the staging and response assessment workup of patients with EMZL.