ctDNA surveillance to detect early relapse in patients with large B-cell lymphoma

Treatment with axicabtagene ciloleucel (axi-cel) has been beneficial to many patients with relapsed/ refractory large B-cell lymphoma (LBCL); however, many patients do not achieve durable remission. Early identification of patients that are likely to progress earlier could allow for more successful interventions. The current method relies on positron emission tomography-computed tomography (PET-CT) serial imaging; however, circulating tumor DNA (ctDNA) has been identified as having potential as a marker of disease progression. Recombination in variable, diversity, and joining gene segments of immunoglobulin genes results in unique markers of clonality, which can be used to monitor B-cell malignancies through cell-free DNA using next generation sequencing.

In a prospective study by Frank, et al. the value of ctDNA monitoring in patients with LBCL was investigated.¹

The Lymphoma Hub recently ran an educational theme investigating the use of ctDNA, the first article can be found here.

Study design

This study included 72 patients and assessed the value of ctDNA analysis before and after treatment with axi-cel.

Eligibility criteria for the study included adults ≥18 years of age who had been:

• diagnosed with diffuse LBCL, transformed follicular lymphoma or primary mediastinal B-cell lymphoma,
• enrolled prior to lymphodepleting (LD) chemotherapy,
• had histology samples available for clonotype identification; and,
• had disease measurable by PET-CT.

The primary endpoints were:

• To assess the ability of pre-lymphodepletion (pre-LD) ctDNA in predicting the progression free survival (PFS) of axi-cel treated patients with LBCL, with ≥6 months follow-up.
• To investigate the association of ctDNA and minimal residual disease (MRD) on Day 28 to predict PFS of patients with LBCL being treated with axi-cel.

The baseline patient characteristics of the 72 patients included in this study are shown in Table 1. Most of the patients included were diagnosed with diffuse LBCL (68%). The median age of those enrolled was 62 years, 35% of patients were ≥65 years, and 60% of patients were male. Patients had received a median of 3 lines of therapy, and 51% had elevated lactate dehydrogenase (LDH).

Table 1. Patient demographics*

Results                                                                                                                 

Survival outcomes and adverse events

The overall response rate was 84.7% and the complete response rate was 63.9%. Median PFS was 10.3 months, median duration of response was 79.5% at one year, and median overall survival was 71.2% at one year.

Recorded adverse events included any grade cytokine release syndrome (CRS) (91.7%) vs Grade ≥3 CRS (5.6%), and any grade immune effector cell-associated neurotoxicity syndrome (ICANS) (55.6%) vs Grade ≥3 ICANS (27.7%). Of the 72 patients included in the study, 96% had sufficient formalin-fixed paraffin-embedded (FFPE) samples for tumor clonotype tracking. Clonotypes were identified from FFPE in 93%, while 7% ultimately required the use of initial plasma samples when clonotypes could not be identified using FFPE tissue.

ctDNA analysis

A significant association was found between elevated LDH levels and high pre-LD ctDNA concentration as compared with normal LDH (p < 0.001). In addition, an International Prognostic Index score of ≥3 vs a score of 0–2 (p = 0.0143) and stage III−IV vs stage I or II disease were also associated with elevated pre-LD ctDNA (p = 0.0196; Table 2).

Table 2. ctDNA concentration association with clinical characteristics*

ctDNA was measured until the patient experienced disease progression, died, or reached one year after therapy. Patients that showed a durable response had a decreased level of pre-LD ctDNA compared with progressing patients (8 [0–1,327] LG/mL vs 581 [0–17,903] LG/mL, p < 0.0001). In total, 70% of responding patients had no measurable ctDNA by Day 7, which became 100% after Day 90.

For most patients experiencing disease progression, there was an initial decrease which reached its lowest point by Day 28 at 6 (0–2,945) LG/ml, this was followed by a subsequent increase. A 1-log reduction in ctDNA concentration was seen in 77% of patients experiencing disease progression, while 52% showed a 2-log reduction at the lowest point compared with baseline. Notably, 39% of progressing patients had at least one sample with undetectable ctDNA levels between Days 7 and 21.

There was a group of nine durable responders and three patients experiencing disease progression that had no detectable ctDNA despite having PET-avid disease when they were enrolled. For the three patients with disease progression, ctDNA became measurable after Days 0, 7, and 90, respectively. For the durable responders, ctDNA levels remained undetectable during the study period.

Risk of relapse and pre-LD ctDNA concentration

The association of the pre-LD ctDNA with risk of relapse or progression was investigated and it was found that ctDNA concentrations >100 LG/ml had an increased risk (Table 3).

Table 3. Correlation of pre-LD ctDNA concentration with survival outcomes*

The association between the risk of developing CRS and ICANS and pre-LD ctDNA concentration was also analyzed. Patients with low grade or no CRS had significantly decreased median ctDNA concentration compared with Grade ≥3 (p = 0.0485). For no or Grade 2 ICANS vs Grade ≥2 ICANS a similar trend was seen (p = 0.0340).

ctDNA surveillance and MRD

On Day 28, ctDNA was measured—along with clinical and radiographic staging—to assess for MRD; detection of any amount of ctDNA was recorded as MRD positive. Of the 72 patients, 60 had samples available for analysis; 50% were durable responders and the other 50% were patients experiencing disease progression. Of the durable responders, 83% were MRD negative. Of the patients experiencing disease progression, 73% were MRD positive.

At least one MRD positive sample was recorded prior to relapse for all 30 of the patients in which the disease progressed.

MRD status was also compared with response measured by PET-CT on Day 28. The four patients who had progressive disease on Day 28 were all MRD positive and had a median OS of 3.2 months. Once these patients were excluded, a significant difference was found between median PFS and OS for MRD negative patients vs MRD positive or those with PET-avid disease (Table 4). Results for patients achieving a complete response were similar to the outcomes for MRD negative patients.

Table 4. MRD status on Day 28 and survival outcomes*

Conclusion

ctDNA shows promise as an early marker for relapse and progression in LBCL patients treated with axi-cel alongside PET-CT evaluation. ctDNA monitoring also has the advantage of being non-invasive. A total of 97% of patients experiencing disease progression had detectable ctDNA levels at the same time they were found to be progressing. In addition, almost all patients became MRD positive prior to relapse, demonstrating that serial ctDNA measurements may be a valuable tool in asymptomatic patients.