Incidence, risk factors and outcome of histological transformation in follicular lymphoma

Histological transformation (HT) into diffuse large B-cell lymphoma (DLBCL) was documented in 37 of the 281 (13%; 95% CI, 9-18) follicular lymphoma (FL) patients treated at our institute from 1979 to 2007. HT occurred at a median of 2.75 similar to years from initial FL diagnosis and HT rate was 15% at 10 similar to years and 26% at 14 similar to years, with a plateau from that point onward. Patients with bulky or extranodal disease, or those diagnosed before 1990 had a significantly higher risk of HT. When initial treatment strategies were taken into account, a reduced HT risk was seen in the patients initially managed with a watch and wait policy, while the risk appeared significantly increased in the small subset of 18 patients initially managed with rituximab plus chemotherapy (P similar to=similar to 0.0005). HT was associated with a significantly shorter cause-specific survival (P similar to=similar to 0.0002). Predictors of survival after HT were the Follicular Lymphoma International Prognostic Index at diagnosis, as well as age and performance status at the time of HT. Our data confirm the adverse clinical outcome of FL after HT. In keeping with previous isolated reports, our findings suggest that there is a subgroup of patients in whom HT may not occur.