Effectiveness of rituximab-containing treatment regimens in idiopathic multicentric Castleman disease

Human herpes virus type 8 (HHV-8)-negative, idiopathic multicentric Castleman disease (iMCD) is a rare lymphoproliferative disease often involving constitutional symptoms, cytopenias, and multiple organ system dysfunction. In China, the majority of MCD cases are HHV-8 negative. Given that siltuximab, the only FDA-approved treatment for iMCD is not available in China; rituximab- and cyclophosphamide-containing regimens are often used in the treatment of Chinese iMCD patients. To evaluate the efficacy of rituximab in this rare and heterogeneous disease, clinical and pathological data from 27 cases of iMCD were retrospectively analyzed from two large medical centers in China. The novel diagnostic criteria for iMCD were applied, and POEMS syndrome, IgG4-related diseases, and follicular dendritic cell sarcomas cases were excluded from analyses. Total response rate of rituximab- and cyclophosphamide-containing regimens was 55.5%, with 33.3% (9/27) of the cases reaching CR and 22.2% (6/27) PR. In the 14 cases of R-R iMCD, total response rate was only 42.9% (CR 14.3% [2/14], PR 28.6% [4/14]). The 5-year OS of these 27 iMCD cases was 81% (95% CI 64-98; 27 total patients, 4 events, 23 censored) after receiving these regimens, but the 5-year PFS was 43% (95% CI 19-66; 25 total patients, 11 events, 14 censored). Thus, rituximab-based regimens should be considered for the treatment of iMCD patients when siltuximab is not available and potentially in siltuximab-refractory cases.