ICML 2017 | Genotyping of classical Hodgkin Lymphoma using liquid biopsy – Hodgkin Lymphoma Session 

During the 14^th International Conference on Malignant Lymphoma (ICML) held in Lugano, Switzerland, a Hodgkin Lymphoma Session, co-chaired by V. Diehl (University of Cologne, Germany) and A. Pavlovsky (Pavlovsky Center for Hematology, Buenos Aires), took place on Thursday 15^th June.

During this session, D. Rossi from the Institute of Oncology Research, Bellinzona, Switzerland, gave a talk on genotyping classical Hodgkin Lymphoma (cHL) using a liquid biopsy (abstract #052).

Thus far, the mutational profile of cHL is poorly characterized and the genetics of refractory disease have not been fully elucidated. Genotyping of tumor tissue is challenging (i.e. tumor representation, FFPE) and interim PET is neither 100% sensitive or specific for defining ultimate patient outcome.

Liquid biopsy is a source of tumor DNA for Lymphoma genotyping. Plasma cell free DNA is easily accessible, allows for real time monitoring, and has already been tested in DLBCL.

The study presented by Rossi aimed to:

• Provide evidence that plasma cfDNA can be used to track the cHL mutational profile
• Characterize the genetics of newly diagnosed cHL and, for comparative purposes, refractory cHL

The study included plasma cfDNA and germline (g)DNA from 29 patients with treatment naïve and 15 patients with chemo-refractory cHL. Paired gDNA from tumor tissue biopsies was available for 17 patients, including 3 cases for which Reed-Sternberg (RS) enriched areas were macro-dissected. Plasma cfDNA, normal gDNA, and tumor gDNA were subjected to targeted ultra-deep Next Generation Sequencing (NGS) by using CAPP-seq and Illumina platforms (sensitivity of 3x10^-3).

Key Highlights:

• Plasma cfNDA genotyping identified non-synonymous somatic mutations in:
  • Newly diagnosed cHL: STAT6 (45%), TNFAIP3 (45%), ITPKB (31%), B2M (21%), GNA13 (17%), and XPO1 (10%) among the most recurrent genes
  • Refractory cHL: GNA13 (36%), ITPKB (29%), ATM (29%), B2M (21%), STAT6 (21%), KMT2D (21%), XPO1 (21%), TET2 (21%), and TNFAIP3 (14%)
• Mutations of TET2 were enriched in refractory cHL patients versus newly diagnosed cases, indicating they contribute to the chemo-refractory phenotype
• Consistently, genotyping of longitudinal samples disclosed the acquisition of TET2 mutations in one patient with refractory disease
• The majority of mutations discovered in cfDNA were also identified in paired tumor DNA from the tissue biopsy and/or macro-dissected RS cells, confirming their tumor origin
• By pathway analysis, the mutational profile indicated the involvement of PI3K/AKT signaling (49%), cytokine signaling (41%), NF-kB signaling (51%), epigenetics (39%), and immune escape (22%) in cHL
• ITPKB (a negative regulator of PI3K) was specifically mutated in cHL across aggressive B-cell Lymphomas
• In RS cells from wild type cases, the ITPKB protein showed a nucleo-cytoplasmic pattern; in RS cells from mutated cases, ITPKB localized only in the cytoplasm, alluding to the mutations resulting in a change in function and alteration of subcellular localization of the protein
• The L-1236 cHL cell line, that harbors a mutated, truncated ITPKB, was resistant to PI3K inhibitors (RP6530 and AEZS136)
• cHL cell lines harboring a wild type ITPKB (L-540, L-428, KM-H2) maintained sensitivity to these compounds

Davide Rossi concluded the talk by stating that cHL can successfully be genotyped using plasma cfDNA. STAT6, TNFAIP3, and ITPKB are frequently (>20%) mutated in cHL. ITPKB mutations (approximately in 30% of cases) associate with pAKT and resistance to PI3K inhibitors. cHL refractoriness does not associate with TP53 mutations but is enriched with TET2 mutations. Clonal evolution in cHL follows a branching pattern. Lastly, dynamic changes in tumor cfDNA may complement imaging in anticipating ABVD outcome.