Conference Abstracts - 2025 Summit on Hematologic Cancers
Vol. 5, Issue Supplement 1, 2025 · S1-2
Quantitative Assessment of the Evolution of Therapeutic Target Antigen Expression Level in Diffuse Large B-Cell Lymphoma in Response to Treatment
Agrima Mian, MD,Meredith Nichols, MD,Wei Wei, MS,Paolo Caimi, MD, MBA,Sarah Ondrejka, DO,Brian Hill, MD, PhD
Submission received: 2025-07-16 / Accepted: 2025-07-28 / Published: 2025-09-23
Introduction
About one-third of patients with diffuse large B-cell lymphoma (DLBCL) experience relapsed/refractory (R/R) disease after frontline rituximab-based chemoimmunotherapy. Loss or downregulation of CD20—and possibly CD19—may contribute to treatment resistance, though incidence estimates vary due to non-quantitative detection methods. We aimed to quantitatively evaluate changes in CD19 and CD20 surface expression from diagnosis to relapse to inform therapeutic targeting.
Methods
We conducted a retrospective review of patients with R/R DLBCL treated with R-CHOP or R-EPOCH. Clinical and pathologic data at diagnosis and relapse were collected. Archived flow cytometry data from tumor specimens were reanalyzed using FCS Express® to quantify fluorescence intensity (FI) of CD19 and CD20. Multivariate linear mixed models compared expression levels between time points.
Results
51 flow cytometry assays (26 diagnostic and 25 at R/R) were analyzed for 33 patients. Paired archival flow cytometry assays (at diagnosis and R/R) were available for 18 patients (36 specimens). Median age at diagnosis was 64 (range, 41-76) years, 24 patients (73%) were male and 29 (88%) had IPI ≥ 2. Cell of origin at diagnosis was germinal center in 16 (49%) and non-germinal center in 12 (36%) patients, while two patients had a double-hit rearrangement at diagnosis. All patients were treated with rituximab-based chemo immunotherapies i.e., R-CHOP (27; 82%) or R-EPOCH (6; 18%). Median time to R/R was 10.4 months. There was a significant reduction in median FI of CD20 from diagnosis [median: 40,610 (range: 167 – 259,962)] to R/R [median: 11,596 (range: 63 – 79,592)], representing a mean reduction of 63% at R/R relative to diagnosis (P= 0.01; 95% CI: 20-73%). Similar change was observed in geometric mean FI of CD20, which was reduced 65% at R/R relative to diagnosis (P< 0.01; 95%CI: 31-82%). Median and geometric mean FI of CD19 at R/R were 38% and 20% lower compared to diagnosis, respectively, but these differences were not statistically significant (P= 0.08 and 0.39, respectively) (Table). When examining the relative change in FI at R/R in individual cases, compared to the mean FI of all diagnostic cases, we observed that 21 out 25 cases (84%) had reduction of CD20 whereas only 14/25 (56%) had reduction of CD19. Interestingly, 7/25 (28%) cases had an increase in CD19 expression by >80% (Figure). CD20 downregulation was significantly associated with age >60, bone marrow involvement, and extranodal disease.
Conclusions
CD20 expression significantly declines at relapse following rituximab-based therapy, while CD19 is largely stable and may increase in select cases. These findings support repeat tissue assessment at relapse, particularly to guide use of CD20- and CD19-directed therapies and clinical trial enrollment.