ALL-10
Patients characteristics
Out of 464 MR patients enrolled in the ALL-10 protocol, MRD data at later timepoints than EOC were available for 271 (see the CONSORT diagram, Figure 1). The mean follow-up time was 10.0 years (range 6.1-13.5 years). No significant differences in sex, age, WBC, immunophenotype (B-lineage versus T-lineage) and CNS status at diagnosis were detected between patients with and without available MRD data (Table 1). The percentage of patients with MRD positivity at EOC did not differ significantly between patients with and without MRD data at later time points, nor did the 6-year RFS (SE) differ (89.2 (95% CI: 86-93) versus 92.1% (95% CI:88-96) respectively, (p = 0.29)).
Thirty out of 271 patients (11.1%) relapsed (24 isolated BM, 4 combined CNS and BM, 2 isolated CNS), 3 (1.1%) died in remission and 1 (0.4%) developed a second malignant neoplasm.
Prognostic significance of MRD at the end of consolidation 1 (EOC) and subsequent time points
At EOC (TP2) all patients had MRD < 0.05% as per protocol definition for intermediate risk patients. At EOC 178 out of 269 (66.2%) patients were MRD negative (undetectable MRD) and 91 (33.8%) MRD positive. Of the MRD positive patients, 80 (29.7%) had positive not quantifiable MRD and 11 (4.1%) had positive quantifiable MRD levels (0.01% < 0.05%). EOC MRD negativity was associated with a better RFS, with a 6 years RFS of 93.1% (89-97) for MRD- negative patients, and 80.3% (72-89) for MRD positive patients (p <0.01), supplementary figure 3a.
We analyzed the 3 timepoints after consolidation1. For each timepoint, patients with negative MRD had a better outcome than patients with positive MRD (supplementary figures 3 b,c,d).
- Value of MRD at later timepoints for MRD negative patients at EOC
From the 178 EOC MRD negative patients, 152 remained MRD negative at later timepoints and 26 patients showed positive MRD results at one or more later timepoints (TP3, TP4, and/or TP5). MRD positivity at later timepoints had no prognostic relevance as both groups had comparable outcomes; 6-y RFS of 92.0% (95% CI:88-97) and 96.2% (95% CI:89-100) for those remaining negative at later timepoints versus those who did not respectively, see figure 2a.
When applying guidelines for therapy intensification, 12 of 26 (46%) patients that showed positive MRD results at one or more later timepoints, were now defined as MRD negative at all subsequent timepoints.
2) Value of MRD at later timepoints for MRD positive patients at EOC
From the 91 patients with positive EOC MRD, 43 were MRD negative at all subsequent timepoints and 48 had a positive MRD result at one or more of the subsequent timepoints (TP3, TP4 and/or TP5). Patients that were MRD negative at all subsequent timepoints had a 6-y RFS of 93% (95% CI:85-100), which is comparable to that of patients being EOC MRD negative mentioned in the paragraph above. However, patients that were MRD positive at later timepoints had a significantly worse 6y RFS (70.5%; 95% CI:58-84, p =0.002 see figure 2a). When applying guidelines for therapy intensification, 5 of 48 (10%) patients that showed positive MRD results at one or more later timepoints, were now defined as MRD negative at all subsequent timepoints. The RFS for these 43 patients was comparable, 6-y RFS 69.4% (95% CI: 56-83), see supplementary figure 4.
All patients with quantifiable disease at TP2 (EOC, n=11), were MRD positive at TP3; 3 with quantifiable disease and 8 with positive not quantifiable disease. At TP3 7/46 MRD positive patients had positive quantifiable disease. Two of these patients also had positive quantifiable disease at TP4. No other patients had quantifiable disease at TP4 and at TP5 none of the patients had positive quantifiable disease.
Validation cohort ALL-9
MRD data were available for 122 patients of the ALL-9 study who had EOC (TP2) MRD < 0.05% (see the CONSORT diagram, Supplementary Figure 1). Seventy eight out of these 122 (64.0%) patients were MRD negative (undetectable MRD) and 44 (36.0%) MRD positive. Of the EOC MRD positive patients, 37 (30.3%) had positive not quantifiable MRD and 7 (5.7%) had positive quantifiable MRD levels (0.01% < 0.05%). Patients with MRD negativity at EOC had a better 6-years RFS (93.6%; 95% CI:88-99) than patients with positive MRD at EOC (83.5%; 72-0.95) (p = 0.029), supplementary figure 5.
Of 120 patients also MRD results at later timepoints were available; 77 patients were EOC MRD negative; and 43 patients were EOC MRD positive. As in ALL-10, we divided the EOC MRD negative group in two groups; patients that remained MRD negative (n=69), and patients that had any positive MRD results at TP3, TP4, and/or TP5 (n=8). MRD positivity at later time points had no prognostic value as both groups had comparable outcomes; 6-y RFS of 94.2% (88-99) and 87.5% (67-100) respectively (p=0.27), see figure 2b.
Also for the EOC MRD positive patients (n=43) we observed the same results as in ALL-10; patients that became MRD negative at all later timepoints (n=17) had an RFS that was comparable to that of patients that were EOC MRD negative (6-y EFS 94.1 (83-100)). However, patients that remained MRD positive at later time points (n=26) had a worse 6y-RFS of 75.4% (60-94), (p =0.008, figure 2b).