Prognostic Role of Very Early Interim FDG PET/CT after One Cycle of Chemotherapy in Diffuse Large B Cell Lymphoma

Purpose: The aim of this study was to evaluate whether early interim FDG PET/CT after one cycle of chemotherapy has prognostic value in patients with diffuse large B cell lymphoma (DLBCL) in comparison to factors of International Prognostic Index (IPI). Material and methods: 51 consecutive patients with DLBCL were prospectively enrolled from 2012-2018. 31 male and 20 female patients were included (mean age ± standard deviation [SD], 54.6 ± 14.5). All patients received rituximab, cyclophosphamide, hydroxydaunomycin, vincristine (Oncovin^®), and prednisone (R-CHOP) chemotherapy and had four PET/CT studies using the same protocol and system: at baseline and after one, three, and six cycles of chemotherapy (PET0, PET1, PET3 and PET6). We measured peak standardized uptake value (SULpeak) and metabolic tumor volume (MTV) of all lymphoma lesions using the threshold 1.5 × mean SUL + 2 SD of liver. The absolute and percent change of SULpeak (absΔSULpeak and %ΔSULpeak) and MTV (absΔMTV and %ΔMTV) from PET0 to PET1 were calculated. Receiver operating characteristic (ROC) curve analysis was used for optimal cut-off of PET parameters. Factors from IPI were included: age, Ann Arbor stage, lactate dehydrogenase (LDH), performance status, and number of extranodal sites. Statistical analysis was done using Cox regression analysis and Kaplan-Meier method. Factors less than P=0.1 on univariable analysis were included in the multivariable analysis. Results: There were 11 (22%) patients who experienced relapse or disease progression in two-year period after completion of R-CHOP therapy. Median interval from end of therapy to recurrence was 5.8 months (range 1.4-18.4 months). Cut-off values of absΔSULpeak, %ΔSULpeak, absΔMTV and %ΔMTV were computed as 6.6 (area under curve [AUC] 0.584), 79.5% (AUC 0.509), 68.6 cm³ (AUC 0.648), and 99.8% (AUC 0.524). On univariable analysis, age, LDH, absΔSULpeak, and absΔMTV were associated with lymphoma relapse or progression. On multivariable analysis, age (Hazard ratio [HR] 4.370, 95% confidence interval [CI] 1.225-15.594, P = 0.023), absΔSULpeak (HR 4.807, 95% CI 1.411-16.372, P=0.012), and absΔMTV (HR 0.033, 95% CI 1.142-24.640, P=0.033) were independently associated with lymphoma relapse or progression. Conclusions: SULpeak, and MTV changes after 1 cycle of chemotherapy were independent prognostic factors for relapse or disease progression after first line R-CHOP chemotherapy. Early changes of metabolic activity and viable tumor volume may be important prognostic factors in DLBCL.

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