Treatment Outcome in Patients with Primary or Secondary Transformed Indolent B-Cell Lymphomas

Background: Histologic transformation (HT) of indolent B-cell lymphomas into an aggressive form can occur simultaneously (primary HT, pHT) or sequentially after a preceding diagnosis of indolent lymphoma (secondary HT, sHT). The clinical course after diagnosis of HT is variable. Objectives: To describe the outcome of treatment in pHT and sHT patients. Methods: We retrospectively analyzed HT cases with an underlying follicular lymphoma, nodal marginal zone lymphoma, extranodal marginal zone lymphoma, lymphoplasmacytic lymphoma, or small lymphocytic lymphoma at our institution. Kaplan-Meier estimates were used to calculate progression-free survival (PFS) and overall survival (OS). Results: Ninety-two HT patients were identified, 38 with pHT and 54 with sHT. In sHT, time-to-transformation was not influenced by the preceding treatment strategy of the indolent lymphoma component. In pHT, median PFS was 61 months (95% CI 27-61), and OS was not reached. In sHT, median PFS and OS was 14 months (95% CI 9-32) and 42 months (95% CI 16-90), respectively. Significant differences between pHT and sHT in PFS (p = 0.002; Hazard ratio [HR] 2.30, 95% CI 1.36-3.91) and OS (p = 0.0001; HR 3.30, 95% CI 1.81-6.03) were observed. Response to treatment for transformation was highly prognostic of PFS and OS (p < 0.0001). Conclusions: The outcome in pHT cases is favorable and signifi-cantly better than in sHT cases. Failure to achieve a remission after treatment for transformation confers a dismal pro-gnosis.