Prognostic Value of the CALLY Index in Diffuse Large B-Cell Lymphoma: Linking Inflammation, Nutrition, and Tumor Biology

Background/Objectives: Diffuse large B-cell lymphoma (DLBCL) is the most common subtype of non-Hodgkin lymphoma and remains incurable in approximately 30–40% of patients despite advances in immunochemotherapy. Although gene expression profiling has improved risk stratification, there is an ongoing need for non-invasive, cost-effective, and clinically practical biomarkers to identify patients at high risk of treatment resistance or relapse (R/R). Systemic inflammation plays a pivotal role in DLBCL pathogenesis, impacting both tumor progression and treatment response. The C-reactive protein–albumin–lymphocyte (CALLY) index, integrating markers of inflammation, nutritional status, and immune competence, has demonstrated prognostic relevance in solid tumors; however, its relevance in hematologic malignancies remains unexplored. Methods: We retrospectively analyzed 180 adults with newly diagnosed DLBCL, NOS (not otherwise specified) who received frontline rituximab-based immunochemotherapy (R-CHOP or CHOP-like regimens) between January 2014 and December 2019 at three tertiary centers in Serbia. The median age was 67 years (IQR 59–73), and 56.1% were female. Receiver operating characteristic (ROC) analysis determined 6.5 as the optimal CALLY index cut-off (AUC 0.744, 95% CI 0.670–0.817; p < 0.001). Results: A low CALLY index (<6.5) was significantly associated with adverse clinical features, including anemia, elevated lactate dehydrogenase and β2-microglobulin, poor ECOG performance status, bulky disease, advanced stage, and unfavorable IPI, R-IPI, and NCCN-IPI scores (all p < 0.001). In contrast, no associations were observed with tumor subtype, immunophenotype, or comorbidities. Furthermore, patients with CALLY <6.5 showed lower overall response rates to treatment (59.6% vs. 85.5%, p < 0.001) and higher relapse rates (21.0% vs. 6.2%, p = 0.014). They also experienced reduced 3- and 5-year overall survival (OS) and event-free survival (EFS) (all p < 0.001). In multivariate analysis, a low CALLY index independently predicted poorer OS (HR 2.04, 95% CI 1.13–3.67; p = 0.017) and EFS (HR 1.89, 95% CI 1.13–3.14; p = 0.015). In addition, it independently identified patients at risk of relapsed/refractory (R/R) disease (OR 2.50, 95% CI 1.02–10.10; p = 0.04), outperforming standard prognostic indices. Conclusions: The CALLY index is a simple, low-cost, and widely accessible biomarker that independently predicts prognosis in DLBCL, NOS. It outperforms standard indices in identifying R/R cases. The CALLY index may enhance risk stratification and guide individualized treatment strategies.