Page 132 - Haematologica June

1034
D. Drandi et al.
Supplementary Table S4. MRD monitoring of this series is graphically depicted in Figure 5. All the treatment-naïve patients were MYD88L265P mutated at baseline (either on BM or PB or both), while 2 relapsed patients (one BM and one PB) scored WT (as false negative results, due to pre- vious rituximab exposure, see below). After therapy, 6/22 informative cases showed MRD negativization on BM (27%) and 17/35 (49%) on PB, further suggesting a faster clearance of MRD from PB than from BM. At subsequent time points, the majority of patients remained MRD-pos- itive (namely, patients 26, 28-31 and 33-35), some remained MRD-negative (patients 14-16, 37, 46 and 48), while a few show alternating results (patients 32, 40 and 50). Given the limited series of patients and the retrospec- tive nature of the analysis, it is difficult to draw conclu- sions on the efficacy of single therapeutic schedules in clearing MRD in WM. However, the high potential of MRD shrinkage of regimens containing either fludarabine or bendamustine (each combined with rituximab) is high- lighted in the Online Supplementary Methods (Online Supplementary Figure S7A-C).
Of note, there were 2 false-negative cases among relapsed patients in this series. Patient 44, who had a base- line BM sample depicted as WT (meaning “MRD nega- tive”), but with a borderline mutated:WT ratio, followed by PB positivity in the first follow-up sample (taken after 3 years). The other false-negative case was patient 45, whose PB relapsed sample was negative at baseline, but
then reverted to positive during the subsequent follow up (“MRD reappearance”).
Additionally, 27 paired PB/plasma follow-up samples highlight the role that ctDNA might have for MYD88L265P mutation detection in pre-treated cases, as well as for MRD monitoring. Of note, 14/27 were concordantly pos- itive and 3/27 concordantly negative, while 9/27 scored positive only in plasma and 1/27 positive on PB but not on plasma. Interestingly, the 9 plasma positive cases “res- cued” by ctDNA analysis showed MYD88L265P levels in plasma comparable to those detected in paired BM sam- ples (see Figure 5: patients 52, 50 and 37).
Discussion
ASqPCR has been widely used for MYD88L265P detection in WM, providing a higher level of sensitivity than Sanger sequencing.6,21 However, the recently developed ddPCR simplifies and improves the accuracy of MRD monitor- ing.24,31
This study describes a new ddPCR tool for MYD88L265P screening and MRD monitoring in WM. Our results can be summarized as follows:
1. ddPCR is a sensitive tool for MYD88L265P detection in WM and provides higher resolution compared to the canonical ASqPCR;
2. MYD88L265P ddPCR assay is particularly useful for reli-
Figure 5. MYD88L265P can be used for disease monitoring. MYD88L265P monitored in 52 patients with at least one follow-up (FU) sample. ctDNA: cell tumor DNA; RE: relapsed at baseline; NT: Naïve to Treatment at baseline; MRD: minimal residual disease; PL: plasma; BM: bone marrow; PB: peripheral blood.
haematologica | 2018; 103(6)