Transformed Waldenström macroglobulinaemia: clinical presentation and outcome. A multi-institutional retrospective study of 77 cases from the French Innovative Leukemia Organization (FILO).

Histological transformation (HT) to diffuse large B-cell lymphoma (DLBCL) is a rare and poorly reported complication of Waldenström macroglobulinaemia (WM). We performed a retrospective study of 77 WM patients with biopsy-proven transformation to DLBCL. The median time from WM diagnosis to HT was 4·6 years and 16 patients (21%) had never been treated for WM. At HT, extranodal sites were observed in 91% of patients with a rather high incidence of central nervous system, cutaneous or testicular involvement. Fluorodeoxyglucose-positron emission tomography was performed in half of the patients and the median maximum standardized uptake value was 15 for transformed disease. More than 80% of cases with available data for assessment by the Hans' algorithm harboured a non-germinal centre B-cell phenotype. First-line treatment for transformation consisted of R-CHOP (rituximab, cyclophosphamide, doxorubicin, vincristine, prednisone)-like regimen in 85% of patients. The overall response rate after first-line treatment was 61% and the median overall survival was only 16 months for the entire cohort. Time to transformation above 5 years (P = 0·0004) and elevated LDH (P = 0·02) were associated with worse outcome. Based on these findings, HT should be considered and lead to a biopsy in WM patients presenting with extranodal involvement, elevated LDH and constitutional symptoms. The optimal therapeutic approaches remain to be defined.