Successful Preemptive Treatment of Molecular Relapse after Autologous Stem Cell Transplantation in Mantle Cell Lymphoma
Authors: Andersen Niels S. , Pedersen Lone B. , Laurell Anna , Elonen Erkki , Kolstad Arne , Geisler Christian H. 
Published: October 2019

Abstract
Autologous stem cell transplantation (ASCT) leads to induction of molecular remission in mantle cell lymphoma (MCL). A large proportion of the patients, however, relapse after ASCT. Increasing levels of minimal residual disease (MRD) in consecutive BM samples after ASCT have been observed prior to relapse by us and others, whereas patients in continuous clinical remission have remaining low levels of MRD. In the present 2nd Nordic MCL Phase 2 trial we aimed to direct preemptive treatment to patients in clinical remission but with increasing levels of MRD at high risk of relapse after ASCT. We used a combined standard nested and quantitative real-time PCR analysis to estimate MRD levels (Andersen et al, 2002, Exp. Hematol). According to the protocol consecutive BM and PB samples were procured and shipped for central PCR analysis every 3–4 months post-transplant. Preemptive therapy consisted of four weekly doses 375 mg/m2 of Rituximab. Of the 161 MCL cases included in the trial 81 cases underwent ASCT and had PCR markers available. CR-rate after ASCT was 92%. In total 852 post-transplant BM/PB samples were monitored for MRD. 47 of 81 (58%) cases remained standard nested PCR negative after ASCT for a median follow-up time of 2.7 years (range: 0.14–5.7 years). In 4 (8%) of these a clinical relapse was observed without any PCR detectable MRD present in BM or PB after ASCT, including at time of clinical relapse. In 34 (42%) of 81 cases standard nested PCR was positive at least once after ASCT. The majority of the PCR positive cases (26/34 cases, 76%) converted from standard nested PCR negative to positive during post-transplant follow-up, thus, these cases relapsed molecularly. 8 (24%) of 34 cases remained standard nested PCR positive after ASCT. In these, a rising level of MRD was detected by real-time PCR analysis in 4 cases. The remaining 4 cases either had stable low or declining levels of MRD. Of the 30 cases which relapsed molecularly 8 cases simultaneously underwent a clinical relapse leaving no therapeutical window for preemptive treatment. One case refused preemptive treatment. All molecular relapse occurred within 3 years after ASCT, except in 1 case. In total 21 cases have received preemptive treatment. 19/21 (90%) cases became standard nested PCR negative (18 cases) or reduced to low MRD level (1 case). 2/21 cases remained PCR positive and relapsed after 3 and 6 months, respectively. 16/21 cases remain in clinical CR for a median follow-up time of 1.4 years after preemptive treatment (range: 0.25 to 3.8 years) and 5/21 cases have relapsed. Of the latter cases the 3 of the 5 became PCR negative for 6–9 months before relapse. Of note, two cases have received preemptive treatment twice after a second molecular relapse after which they again became PCR negative. Preemptive treatment has not been reported in lymphoma before. Our results in MCL suggest that the large number of cases who remain in molecular remission after intensified ASCT may be followed by MRD monitoring and treated at molecular relapse instead of receiving maintenance therapy. However, 4 of these cases relapsed. Here, more than PCR methods are needed for early stage disease detection. Our results indicate that preemptive treatment using Rituximab can successfully reinduce molecular remission and prolong time to relapse. Finally, more patients may have PCR markers available by applying frozen diagnostic lymph node material.