Molecular Characterizations of Diffuse Large B-Cell Lymphoma

Anas Younes, MD

Today, we are speaking with Dr. Anas Younes about recent developments in molecular characterizations of diffuse large B-cell lymphoma and clinical trials for this type of lymphoma. Dr. Younes is a medical oncologist and the chief of the Lymphoma Service at Memorial Sloan Kettering Cancer Center in New York City where he specializes in the treatment of lymphoma and conducts clinical trials.

-Interviewed by Anna Azvolinsky, PhD

OncoTherapy Network: First, Dr. Younes, can you talk about how genetic sequencing and also gene expression data analyses, how these have helped to evolve, and how we define diffuse large B-cell lymphoma?

Dr. Younes: Sure. So, over the last 3 decades, we have been used to classifying lymphoid malignancies and cancers in general based on the appearance, under the microscope, and immunohistochemistry. And as we base therapy on these characteristics, we all learned that some patients do respond and some don’t respond well to certain drugs even though these tumors all look the same under the microscope. And that, of course, suggested that there is tumor heterogeneity beyond just simply appearance and everyone started to examine these characteristics. And the first thing was looking at the gene expression profiling and we learned, which is not surprising, that diffuse large B-cell lymphoma can be subclassified into at least two broad segments or categories based on what we call the cell of origin.

The one big category is the ABC or activated B-cell type of B-cell lymphoma and the other one is called the germinal center cell type or GCB diffuse large B-cell lymphoma. And there are about 15% to 20% of the diffuse large B-cell lymphomas that fall in between these two categories and they are called unclassified. And why is this important? This is important because prognostically, it could predict who is likely to benefit from standard of care chemotherapy, which for us, it’s called R-CHOP. So, for patients with diffuse large B-cell lymphomas, the GBC subtype, have a higher cure rate compared to those with the ABC subtype. So, with this knowledge then, many investigators and sponsors felt that patients with the ABC subtype have more of an unmet medical need and therefore, started to select patients for clinical trials based on the ABC subtype.

OncoTherapy Network: Based on what we know about these molecular subtypes, can you highlight some of the new drug treatment strategies that are in development? I am guessing that the trials that are categorizing DLBCL into these subtypes are relatively new?

Dr. Younes: Right. So, from a prognostic point of view, as I mentioned, we learned that diffuse large B-cell lymphomas of the ABC subtype has more of an unmet medical need and therefore, clinical trials started to focus on this subpopulation. But also, we learned from diving into the gene expression profiling data and from subsequent molecular analyses including DNA sequencing studies, suggested that the ABC subtype has more dependency on the NF kappa B survival mechanism and therefore, suggested that agents that could disrupt this pathway may contribute to improved treatment outcomes.

So, as we have seen over the last few years, clinical trials with a randomized trial design compared the standard R-CHOP to R-CHOP plus drug X and drug X was typically selected based on its ability to disrupt NF kappa B pathway at different levels, whether it is bortezomib or agents that inhibit B-cell receptor signaling like ibrutinib.

OncoTherapy Network: You mentioned a third, amalgamation subtype of diffuse large B-cell lymphomas that is not well characterized. Have there been recent developments to understand the biology of these tumors and whether there are distinct subtypes within that group?

Dr. Younes: So, this unclassified group which accounts for about 15% to 20% of the diffuse large B-cell lymphomas, the reason it is called unclassified is because, again, the classification is based on gene expression profiling of hundreds of genes. So, the pattern would be that hundreds of genes are turned on or turned off that distinguish between ABC and GCB subtypes. But there is a transition situation where some of the genes are turned off and some are turned on while they are transitioning from ABC to GCB subtypes, and that is what is called the unclassified type. From gene expression profiling, this group is halfway between ABC and GCB. However, this category disappears when you try to use a surrogate clinical diagnostic test to divide diffuse large B-cell lymphomas into again, molecular subtypes.

So, using gene expression profiling, we get ABC, GCB, and unclassified subtypes. If you use different immunohistochemical algorithms, you can capture the GCB, but you can’t capture the ABC in its true form. You capture the ABC and unclassified types in one category that we call the non-GCB and that is what you will see when you read papers or clinical trial eligibility criteria. We use these terms in different situations-so we say either GCB or ABC. That means we are using gene expression profling or we use the term GCB and non-GCB, and that is when we use immunohistochemistry methods.

OncoTherapy Network: Ok. And just lastly, what are some of the major questions, biological or clinical, that are important to address in diffuse large B-cell lymphoma.

Dr. Younes: So, although the gene expression profiling-based classification of GCB and ABC was a major step forward in terms of better understanding the biology and dividing the disease into two different prognostic groups that can help guide therapy, we understand that this is probably overly simplistic and not sufficient to guide therapy with precision. So, different centers started to do DNA sequencing of lymphomas, including diffuse large B-cell lymphoma, we found that even the ABC and GCB subtypes are very heterogeneous based on different genetic alterations.

So, what is happening right now, which is the future, is to divide these broad categories into smaller subsets that are better defined based on more precise genetic alterations that can guide therapy with more precision. As an example, you can envision patients with CREBBP/EP300 mutations that can be treated with treatment A, patients with CD79B mutations can be treated with drug B, and patients with p53 mutations can be treated with drug C, and so forth. So, we are moving away from the ABC and GCB classification to more precisely defined subsets based on the molecular alterations.

OncoTherapy Network: Thank you so much for joining us today, Dr. Younes.

Dr. Younes: Sure, it’s a pleasure.