Allogeneic Hematopoietic Stem Cell Transplantation in Transformed Follicular Lymphoma (tFL): Results of a Retrospective Multicenter Study from GELTAMO/GETH-TC Spanish Groups

SIMPLE SUMMARY: Follicular lymphoma (FL) is the most prevalent subtype of indolent lymphoma, accounting for 70% of all cases. The estimated risk of histological transformation (tFL), such as diffuse large B cell lymphoma (DLBCL), varies from 2–3% per year to 7–8% at 10 years in different series. Treatment after transformation is not clearly established. Allogeneic hematopoietic stem cell transplantation (alloSCT) could be an option for these patients, but it has not been widely explored. We analyze the efficacy and toxicity of alloSCT in 43 patients from 14 Spanish centers. We observed long-term survival in around one third of the patients, especially those who developed chronic graft versus host disease, indicating that alloSCT continues to be a potentially curative option for patients with tFL, mainly due to the graft versus lymphoma effect. ABSTRACT: Background: Transformation of follicular lymphoma into an aggressive lymphoma (tFL) worsens the prognosis and the standard treatment is not completely defined. Allogeneic hematopoietic stem cell transplantation (alloSCT) could be a potentially curative option for these patients, but it has not been widely explored. Methods: We designed a retrospective multicenter study to analyze the efficacy and toxicity of alloSCT in tFL patients and potential prognostic factors of survival. Results: A total of 43 patients diagnosed with tFL who underwent alloSCT in 14 Spanish centers between January 2000 and January 2019 were included. Median age was 44 (31–67) years. After a median follow-up of 58 months, estimated 5-year overall survival (OS) and progression-free survival (PFS) were both 35%. Estimated 100-day and 1-year non-relapse mortality (NRM) were 20% and 34%, respectively. The type of conditioning regimen (3-year OS of 52% vs. 20%, respectively, for reduced-intensity vs. myeloablative conditioning) and development of chronic graft versus host disease (cGVHD) (3-year OS of 75% vs. 40%) were the only factors significantly associated with OS. The only variable with an independent association with OS was cGVHD (HR, 3.4; 95% CI, 1.2–9.6). Conclusions: Our results indicate that alloSCT continues to be a potentially curative option for patients with tFL.