Radioimmunotherapy Is Safe and Effective in Relapse after Stem Cell Transplantation for B- Cell Non Hodgkins Lymphoma, An Analysis of the International RIT-Network
Authors: Hohloch Karin , Zinzani P.L. , Linkesch Werner , Deptala Andrzej , Wojciech Jurczak , Suh Cheolwon , Lorsbach Michael , Windemuth-Kiesselbach Christiane , Truemper Lorenz H. 
Published: April 2020

Abstract
Background: Autologous stem cell transplantation produces prolonged disease free survival in patients with relapsed or refractory Non Hodgkins Lymphoma (NHL), although relapse remains the most common cause of treatment failure. Radioimmunotherapy (RIT) is a novel treatment option for NHL patients combining immunotherapy and radiation. However, there are only sparse data available on the safety and efficacy of radioimmunotherapy for relapse after autologous stem cell transplantation (ASCT).
Methods: The RIT-Network, started in December 2006, is a web-based, international registry that collects real-world, observational data from RIT-treated patients (pts) with malignant lymphoma from across the world. To date, data of 680 pts treated with RIT have been entered into the database. 78 pts who have received RIT (primarily ibritumomab tiuxetan) following a stem cell transplantation are documented in the registry, 50 pts with follicular lymphoma (FL) and 28 pts. with other histologies. 62 pts with a follow up of &gt; 12 months are included in the following analysis.
Results: 62 pts (42 with and 20 with other histologies: 2pts. B - CLL, 10 pts. DLBCL, 1pt. lymphoplasmacytic, 5pts. mantle cell, 2 pts. nodal marginal) are included in the analysis. Median age at primary diagnosis was 48 years (range 23 to 68 yrs). Tumor stage showed 3 pts. stage I, 7 pts. stage II, 19 pts stage III, 32 pts. stage IV, for 1 pt. tumor stage is not 1 documented. 40 % of the pts. had previous radiotherapy, 48% of the pts. 1–3 previous Ctx., 45% 4–6 previous Ctx. and 7% had more than 7 previous Ctx. 57 pts. had one previous ASCT and 4 pts. had 2 previous ASCTs. 8 patients had already undergone RIT previously. RIT was used as second line therapy in 6 pts., third line in 13 pts., fourth line in 15 pts., fifth line in 18 pts. and &gt; sixth line in 6 pts. The indication for most of the patients was recurrence (31 pts.) consolidation (13 pts.) and therapy refractory (11 pts.). Best response was CR in 21 pts (34%), PR in 15 pts. (24%), SD in 3 pts (5%) and PD in 13 pts. (21%). Haematotoxicity is not documented for all patients. Median nadir for haemoglobin (Hb) (n=46), neutrophils (ANC) (n=40) and platelets (plts) (n=47) was 8.95 g/dl (range 4.1 to 15.1g/dl), 1,3/μl (range 0–2290 ANC/μl) and 89 μl (range 8 – 150 000 tplst/μl) respectively. Time to nadir was 49 (range 1 to 400), 45 (range 13–412) and 34 (range 14 to 404) days for Hb, neutrophils and plts, respectively. Complete recovery of blood count was reached in median on day 133 (range day 28–467 days).
Conclusion: RIT is a feasible and safe treatment modality for patients who relapsed after autologous stem cell transplantation for relapsed or refractory NHL. RIT shows encouraging results with a CR rate of 34% in this non-interventional registry analysis. Haematotoxicity seems to be increased in comparison to first- or second line RIT. Prospective clinical trials in this patient population are warranted.