Prognostic value of minimal residual disease detection by circulating tumor DNA in Hodgkin lymphoma.

Abstract INTRODUCTION: First-line treatment is curative in more than 80% of patients with Hodgkin lymphoma (HL). However, ~20% of cases relapse or progress due to the persistence of undetectable active tumor cells (known as minimal residual disease, MRD), and currently we cannot identify this subgroup of patients with enough precision and anticipation. Response assessment in HL is currently based on positron emission tomography (PET); however, sensitivity and, particularly the specificity of PET-based response assessments can be limited. Overall, there is a high unmet clinical need for better biological risk classification and novel response assessment in HL. Detecting circulating tumor DNA (ctDNA) is a tool that allows for diagnostic molecular profiling, response assessment and monitoring of minimal residual disease (MRD). OBJECTIVES - To analyze a series of patients with newly diagnosed HL using ctDNA to identify molecular markers of the tumor. - To evaluate MRD after two cycles of treatment using highly sensitive ctDNA techniques, to compare the results with those of PET/CT and to assess its prognostic impact on final response and survival. MATERIALS AND METHODS - Patients: HL diagnosed between 2017 and 2021 in Castile and León. - Samples: peripheral blood at baseline (n=74) and after two cycles of treatment (PET2) (n=45). - Methods: Circulating DNA (cDNA) was analyzed using a custom Next Generation Sequencing (NGS) capture panel including 46 genes related to HL. Unique molecule identifiers (UMIs) were employed to increase sensitivity and reducing sequencing artifacts. - PET/CT evaluation was performed by using the Deauville score. RESULTS At diagnosis, adequate cDNA was obtained in 65/74 (88%) patients, and tumor-specific mutations were identified in 45/65 (69%) for MRD follow-up. After baseline and PET2 NGS studies, evaluable results were obtained in 42 patients. The median age was 35y (range 15-76), being 58% of them male and younger than 60y (80%). 35% of them were at early stage, with 16% stage III and 49% stage IV. The histological classification was Nodular lymphocyte predominant HL in 4.4%, Mixed Cellularity in 29%, Nodular Sclerosis in 55.6%, Lymphocyte-Rich HL in 6.6% and unclassifiable in 4.4%. ECOG was 2 or higher in 16% of cases and a bulky disease was annotated in 16% as well. B symptoms at diagnosis were seen in 56% of cases. First-line treatment was ABVD based therapy in all cases, with 13% experiencing some modifications based on the age and comorbidities. Only 4% were escalated to eBEACOPP after PET2(+) results. Thirteen patients (24%) received combined radiotherapy. Genotyping revealed somatic variants in the following genes: SOCS1 (58%), IGLL5 (40%), B2M (33%), GNA13 (31%), STAT6 (29%), ITPKB (28%) and TNFAIP3 (27%). At the time of PET2, we obtained an MRD(–) result by NGS in 34/42 patients (81%), while PET2 was negative (Deauville 1-3) in 26/42 (62%). Of the 42 patients with results from both techniques, 32 (76%) were concordant. Among the 10 discordant cases, one was MRD(+)/PET2(–) (relapsed at 72 months), and nine cases showed MRD(–)/PET2(+), of which 3 of them relapsed at 18, 20, and 46 months. Of the patients who had a positive PET2, only two were subsequently treated with intensified chemotherapy regimens (BEACOPP). Regarding progression-free survival (PFS), PET2(–) patients displayed significantly superior PFS than PET2(+) patients (92% vs. 50% at 3 years, p<0.05). Overall survival (OS) also showed this trend, although not reaching statistical significance (100% vs. 74% at 5 years, p=0.056). Furthermore, MRD(–) patients showed statistically significant differences compared to MRD(+) patients in both PFS (88% vs. 25% at 3 years, p<0.001) and OS (100% vs. 45% at 5 years, p<0.001). Combining PET2 and MRD strategies, 3 prognostic groups were identified with a 3-year PFS of 92% (–/–), 73% (+/–) and 17% (+/+) (p<0.001). CONCLUSION:Finally, we confirm that combining PET/CT & MRD assessment by cfDNA sequencing improves prognostic stratification of HL patients.