Prognostic Value of Interim PET/CT in Predicting Outcomes of Newly Diagnosed Diffuse Large B-Cell Lymphoma Patients Treated with R-CHOP Therapy: A Retrospective Analysis from Single Centre, Riyadh, Saudi Arabia
Authors: Alharbi Asim A , Alsakkaf Abdullah , Alrajhi Abdullah M. , Alhalouly Tahani , Albtoosh Bilal , Alzahrani Kamal , Alnoamani Mohammed S , Alshehri Hassan , Alshehry Nawal F , Motabi Ibraheem H , Marei Mohammed , Alhumaid Muhned , Tailor Imran K 
Published: December 2024

Introduction:
Diffuse Large B Cell Lymphoma (DLBCL) is the most prevalent subtype of Non-Hodgkin's Lymphoma (NHL) and the treatment consists of rituximab plus cyclophosphamide, doxorubicin, vincristine and prednisone (R-CHOP) with cure rates of up to 70% (Kazuhiro Kitajima 2019), However unlike Hodgkin's Lymphoma, role of interim positron emission tomography/computed tomography (PET/CT) in DLBCL is still uncertain. We aim to study the predictive prognostic value of interim PET/CT in theses group of patients.
Methods:
A retrospective data was collected from January 2021 to December 2023 at large tertiary center in Riyadh, Saudia Arabia. 75 patients included with Biopsy-confirmed Diffuse Large B Cell Lymphoma (DLBCL), who were treated with R-CHOP, PET scans were done at the diagnosis, mid treatment assessment with interim PET/CT after the third cycle of R-CHOP, and End-PET at the end of therapy. However, 14 patients did not have an interim PET scan for multiple reasons, and they were excluded. PET scan results were interpreted following the Deauville 5-point scale (D5-PS) criteria. PET was categorized as positive which represents scores of 4-5 or negative which represents scores of 1-3 (complete metabolic remission; CMR). The primary endpoint of the study was progression-free survival (PFS).
Results:
This study included 75 patients (44 males, 31 female) with median age of 51 (range 17 to 93). 44 (59%) of the patients were in advanced stage (III, IV), and 31 (41%) were in early stage (I, II). 24 (31%) patients were having bulky disease.
The overall survival (OS) for whole cohort at two years was 77.2% (95% CI: 65.4% to 85.4%) and the progression-free survival (PFS) was 74.1%, (95% CI: 62.3% to 82. 7%). The overall survival (OS) at two years for patients who achieved CMR at the end PET assessment was 100%, while those who did not achieve CMR had an OS of 31.8% (95% CI: 14.4%-50.8%). PFS at two years was 97.6% (95% CI: 83.9%-99.7%) for patients who achieved CMR at the end PET assessment and 28.6% (95% CI: 12.6%-46.9%) for those who did not.
For patients with interim PET showing CMR, the OS was 77.0% (95% CI: 57.5%-88.4%), but those with positive interim PET was 71.8% (95% CI: 49.7%-85.5%). The PFS for interim PET showing CMR was 75.6% (95% CI: 56.9%-87.1%,) and 69.2% (95% CI: 47.8%-83.3%,) for those with positive PET.
22 (29%) patients had positive interim PET, but 14 (18.6%) of them achieved CMR at end PET. 8 of 22 who did not achieve CMR at the final PET had OS of 41.7% (95% CI: 15.2%-66.5%), PFS 33.3% (95% CI: 10.3%-58.8). 14 of 22 patients with positive interim PET but achieved CMR the final PET had OS and PFS of 100% respectively. The median survival was 0.15 years (95% CI: 0.03-NA, p = 0.0003) for patients who did not achieve CMR, while it was not reached for those who achieved CMR.
When analyzing the impact of germinal center B-cell (GCB) status, OS was 81.8% (95% CI: 63.9%-91.4%) for non-GCB and 72.1% (95% CI: 55.0%-83.6%) for GCB subtype. PFS was 74.6% (95% CI: 55.3%-86.5%) for non-GCB and 72.0% (95% CI: 55.0%-83.5%) for GCB.
In univariate analysis, significant predictors for PFS included complete remission at final PET (HR: 0.01881, 95% CI: 0.00241-0.1467, p &lt; 0.0001), while age at diagnosis, B symptoms, interim PET response, stage, and GCB status were not significant predictors.
Conclusion:
This retrospective study highlights the prognostic value of interim PET/CT scans in predicting PFS in these group of patients. The two-year PFS for patients achieving CMR at interim PET was higher than those with positive interim PET but statistically not significant. Our study also demonstrates that achieving CMR at the final PET scan is the single most significant prognostic factor for both overall survival (OS) and progression-free survival (PFS). Results of this study although small in number, however it conclude that, response on End-PET assessment determines the outcomes of these patients, while positive Interim PET not necessarily a poor prognostic marker if End-PET assessment negative unlike Hodgkin lymphoma, thus questioning its role in DLBCL routine practice.