Role of Serial Positron Emission Tomography (PET) Scans in Indolent Lymphomas' Management - Interim Results from an Ongoing Prospective Study at King Fahd Medical City, Riyadh, Saudi Arabia

Background:

Indolent lymphomas (ind-LYM) are a subset of B-cell lymphomas, characterized by slow growth, protracted course without treatment and a tendency to reoccur after therapy. The management of ind-LYM is varied and evolving. To-date reliable tools for imaging based prognostication and treatment strategies are limited. We explored the utility of serial FDG PET scans (baseline (BL), interim/6 months (INT) end of therapy/1 year (EOT)), in managing ind-LYM).

Methods:

From an ongoing prospective study, examining the role of PET scan in ind-LYM at our institution, we performed an interim analysis of all patients hitherto enrolled in our study. Patients diagnosed as ind-LYM and having undergone serial PET scans from 2015 to date (N=40, males= 27, females =13) had median age of 59.68 ± 14.5 (28-82 at diagnosis. All PET scans were obtained per accepted protocols. SUVmax and Deauville scores (DS) were obtained from five target lesions. The average of composite SUV (cSUV) and composite Deauville scores (cDS) were computed for each patient. Statistical analyses (using t-test, mean delta change) were performed with the cSUV and cDS.

Results:

The types of ind-LYM were CLL/SLL (17), Follicular (15), mantle cell (3), marginal zone lymphoma (3), and 1 each of MALT and lymphoplasmacytic lymphoma. The data were analyzed for two arms of the study treatment chemotherapy arm (CHEMO-22/40) and Rituximab + observation arm (OBSR-18/40). At BL, patients on CHEMO had significantly higher cSUV and cDS compared to those who were on OBSR (SUV: 6.99 vs. 4.32 p-value 0.0124; cDS: 4.37 vs 3.71 p-value 0.0075 respectively). Although there was a delta change in the cSUV and cDS in both arms after INT and EOT, both treatment lines showed no significant difference in the SUV mean and DS (p-value: 0.754 and 0.5721, receptively). A 2-tailed T-test was used for delta change of cSUV. BL to INT cSUV was statistically significant (p-valve 0.05) and difference in cSUV was not significant for BL to EOT (p-valve 0.98). Difference in cDS was not significant between BL, INT and EOT.

Conclusion:

The higher cSUV/cDS at BL for the treatment arm may be due to disease profile at the time of presentation and/or selection bias. At EOT no difference in both estimates were noted. Both arms showed similar trends in delta change from BL-INT-EOT. Our findings suggest that SUV and DS at BL maybe an independent criterion for treatment selection in ind-LYM.