Daratumumab-induced lymphopenia predicts adverse events and outcomes in patients with myeloma.

Abstract

e20534 Background: Daratumumab, a monoclonal antibody against CD38, is very effective in patients with Multiple Myeloma (MM). CD38 is expressed on MM cells but also on normal lymphocytes. Therapy-induced lymphopenia has been reported in 30-40% of patients; however its clinical significance is vastly unexplored. Methods: Here, we report the baseline characteristics and clinical course of 100 relapsed/refractory MM patients treated at the Ohio State University with Daratumumab as single agent or in combination. Data pertaining to patient demographics, MM characteristics, absolute lymphocyte count-ALC, infections, and hospital stays were collected. ALC of less or equal to 500 cells/µL is considered severe lymphopenia. Results: Fifty-nine percent of patients who completed treatment with Daratumumab (59%) developed severe lymphopenia. MM type (LLC and IgA), combination with immunomodulatory drugs (IMIDs), and lower baseline ALC count were statistically associated with severe lymphopenia, while stage, age, cytogenetics, number of prior lines of treatment, and autologous stem cell transplant were not. Patients with severe lymphopenia had higher rates of infections (52.5% versus 41.4%) and required hospital stays more frequently (83.8% versus 52.9%) than patients without severe lymphopenia. Upper respiratory tract infections and pneumonias were the most common infections. Sixty-one percent of severely lymphopenic patients recovered to ALC > 500 lymphocyte/μL while on therapy. The median time to recover was 14 days (average 43 days). Older patients have longer ALC recovery time (average: 52 days versus 24 days). No statistically significant difference in progression-free survival (PFS), overall survival (OS), or overall response rate (ORR) was noted between patients who did or did not develop severe lymphopenia. However, when the severe lymphopenic group was stratified based on ALC recovery, those with persistent lymphopenia had worst OS (p = 0.0019) and PFS (p < 0.0001), possibly due to better immune-mediated anti-tumoral effects. Conclusions: In our patient population, we discovered an elevated rate of severe lymphopenia, hospital utilization, and infections. Persistent severe lymphopenia is associated with shorter PFS and worst OS. Combination with IMIDs and low baseline ALC count are risk factors for severe lymphopenia while patients older than 65 has a longer ALC recovery time. These findings underline the importance of monitoring lymphocyte count and considering prophylactic measures in high-risk patients treated with Daratumumab.