Marginal zone Lymphoma (MZL) is the third most abundant lymphoma and it is subclassified into 3 entities: splenic, nodal and extranodal mucosa associated lymphoid tissue (MALT). Positron emission tomography (PET) using 18F fluorodeoxyglucose (FDG) with computed tomography (CT) is increasingly used for staging and response assessment of FDG avid lymphomas, such as diffuse large B cell lymphoma and Hodgkin lymphoma. The role of PET/CT in lymphomas with variable FDG avidity, such as MZL, is still under active research.
The purpose of this study was to evaluate PET/CT as a diagnostic and prognostic tool in patients with MZL.
A retrospective cohort study of patients with newly diagnosed MZL, treated with immunotherapy, chemotherapy regimen, surgery or eradication between 2008 and 2016 in a single tertiary center. Patients who did not undergo pre-treatment PET/CT (P-PET/CT) were excluded.
Patients were identified through the hospital's computerized database. Demographic, clinical and laboratory data were collected from patients' files until the latest follow-up available and for at least 12 months after completion of treatment administration. P-PET/CT, interim (I-PET/CT) and end-of-treatment PET/CT (E-PET/CT) studies were centrally reviewed by a nuclear specialist and reported using 3 methods of evaluation: visual assessment, maximal SUV reported and Deauville 5-point score (DS) evaluation (DS only for I-PET/CT and E-PET/CT). PET/CT was interpreted as positive if any of the three evaluation methods was positive. The primary outcome was to evaluate the prognostic role of P-PET/CT, I-PET/CT and E-PET/CT on progression free survival (PFS) and overall survival (OS). Survival curve was calculated using the Kaplan-Meier method, and Cox regression. Models adjusted for age, sex, and stage were used to estimate hazard ratios (HR) and 95% confidence intervals (CI) was used for the association between PET/CT positivity, PFS and OS.
Results: Data of 196 patients with MZL were identified. 86 patients were excluded due to absence of P-PET/CT. Thus, 110 patients were included in this analysis. The most frequent histological type of MZL was MALT (51%). Median patients' age was 67 years (range: 18-93). The median follow-up period was 63 months (range: 3-278). 54/110 (73%) presented with bone marrow involvement and 100/110 (91%) had extranodal involvement. MZL transformed to an aggressive lymphoma in 3% of the patients. The median OS and PFS for the whole cohort were 63 months (interquartile range: 39-85) and 60 months (interquartile range: 37-76), respectively. 77/110 (71.3%) patients had positive P-PET/CT. Among 19 patients that had I-PET/CT, eight studies were positive and 11 negative. 63/110 patients underwent E-PET/CT: 12 studies were positive and 51 negative.
P-PET/CT and I-PET/CT were not predictive of PFS or OS. Sub-group analysis of the different types of MZL did not show such a correlation as well.
When adjusted for age, sex and stage, positive E-PET/CT was associated with reduced PFS with a hazard ratio (HR) of 4.16 (CI 1.55-11.2, p=0.005) (Figure 1). Conversely, positive E-PET/CT did not correlate with OS maybe due to the low death rate (3 patients). In a univariate analysis, beta 2 microglobulin was prognostic for PFS with and adjusted HR of 1.44 (CI 1.08-1.94, p-0.014).
Our study shows that above 70% of MZL are FDG avid. P-PET/CT and I-PET/CT were not predictive of PFS; However, E- PET/CT was predictive of PFS with an adjusted HR of 4.2.
Figure 1: The association between E-PET/CT in PFS
No relevant conflicts of interest to declare.
Asterisk with author names denotes non-ASH members.