European Project for ctDNA Detection as a Biomarker for Non-invasive Therapy Monitoring in Paediatric Classical Hodgkin Lymphoma

Classical Hodgkin lymphoma (cHL) accounts for 15% of all cases of cancer in children and adolescents and represents the first cause of cancer during adolescence. Combined multi-modal chemotherapy and modern radiation techniques have transformed cHL in a highly curable cancer. However, up to 10-15% of patients still experience recurrent or primary refractory disease. Thus, there is an unmet need for unravelling the underlying mechanisms of treatment failure and refractoriness in paediatric cHL. Further refinements of treatment strategy are still needed to improve treatment results both in relapse and refractory (R/R) patients and to reduce long-term morbidity and mortality treatment related. Therefore, two main objectives arise: to improve early detection of patients with a high relapse risk to potentially intensify the first line treatment and to better identify low risk patients to further reduce the treatment burden in this good-prognostic population. Initial disease stratification and long-term outcome predictions remain a challenging issue in the field. PET/CT is currently the reference imaging method for initial staging and improves detection of extra nodal disease. None of previous prognostic factors accurately identify patients who will respond adequately and therefore limit the ability to identify patients who should require treatment that is more intensive or new therapeutic approaches like immunotherapy. Taken together, these data emphasize a clear unmet need in the field of cHL. We aim to develop a biomarker tool, which could sharpen the initial risk stratification, improve the assessment of disease evaluation during the treatment and beyond and facilitate the detection of relapse. Over the past decade, as in other malignancies the potential of quantification of circulating tumour DNA (ctDNA) or liquid biopsy, in circulating cell-free DNA (cfDNA) that comprises DNA fragments released from apoptotic or necrotic cells into circulation, has emerged as a promising tool for diagnosis and exploration of the genetic landscape associated with HRS and for response evaluation. Experiences of ctDNA in cHL was first reported in adult cHL. These previous studies paved the way for ctDNA implementation in cHL. First, they contributed to confirm the feasibility to use ctDNA in the detection of tumor-associated mutation. Using paired samples of ctDNA and tumor DNA from HRS cells obtained by microdissection they confirmed the consistent correlation between these two methods. Second, they highlighted the potential role of ctDNA as a surrogate marker for tumor baseline assessment and more importantly for interim evaluation reporting an excellent correlation between the PET/CT result and the presence or the absence of ctDNA after 2 cycles of chemotherapy. Furthermore, Sobesky et al. previously reported that cured patients who were inconsistently judged as interim PET/CT-positive had a more than 2-log drop in ctDNA, whereas relapsing patients who were inconsistently judged as interim PET/CT negative had a less than 2-log drop in ctDNA. These data suggest that ctDNA could be a relevant adjunct to conventional PET/CT approach.