P029 | SECONDARY HYPOGAMMAGLOBULINEMIA IN NON-HODGKIN LYMPHOMAS: INCIDENCE, RISK FACTORS, AND CLINICAL IMPACT

The most frequent form of secondary immunodeficiency (SID) is secondary hypogammaglobulinemia (SAD), commonly caused by B-cell non-Hodgkin lymphomas (NHL) and their treatments. SAD is diagnosed by low serum IgG levels: mild-moderate (4–6 mg/dL) and severe (<4 mg/dL), and is associated with severe, persistent, or recurrent infections. Despite its clinical relevance, SAD in NHL patients remains poorly characterized. We analyzed data from 131 NHL patients (44 LPL, 44 DLBCL, 43 FL) treated at two North Italian Hematology Units. The primary aims were to assess SAD incidence and its clinical impact by correlating IgG levels with infection rates, antibiotic use, and hospitalizations. Incidence curves were generated for the full cohort and stratified by histological subtype. Statistical analyses included exploratory and targeted tests on both continuous and categorical variables. SAD incidence increased after diagnosis, plateauing at 100 months. LPL patients had a significantly higher incidence than DLBCL and FL (p=0.01; no difference between DLBCL and FL, p=0.32). Lower IgG levels correlated with more infections (p=0.0018) and antibiotic use (p=0.0026), though not with hospitalizations. SAD occurred more frequently post-chemotherapy (p<0.0001). Each 1 mg/dL decrease in baseline IgG (p<0.0001) and each anti-CD20 dose (p=0.03) increased SAD risk. No clinical or biological differences were observed between patients who spontaneously recovered immune function and those who remained hypogammaglobulinemic. LPL subtype, higher anti-CD20 exposure, and low IgG at diagnosis were key SAD risk factors. These findings underscore the need for early identification and close monitoring of IgG levels in NHL patients, particularly those receiving anti-CD20 therapy, to reduce infection-related complications.