Elaine Jaffe, MD, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, discusses the importance of the nuances of evolving differing classification systems of lymphoma, focusing on diffuse large B-cell lymphoma, follicular lymphoma, neoplasms, and more, as defined by the International Consensus Classification (ICC) and the World Health Organization (WHO).

These expert insights Research results were presented as “Evolution in the Classification of Lymphoma: From WHO to ICC – where do we go from here” at the 2024 Pan Pacific Lymphoma (PPL) Conference in Lahaina, Hawaii.

Transcript:

Hello, I'm glad to talk with you today. My name is Elaine Jaffe. I'm a principal investigator at the National Cancer Institute and head of the hematopathology section. I'll be talking at the Pan Pacific Lymphoma meeting in Maui on the evolution in the classification of lymphoma. Today we're dealing with a lot of changes in the classification of lymphoma.

Since 2001, we've all used the WHO classification with the third edition published in 2001, and updates published in the fourth and revised fourth edition. In 2022, [International Agency for Research on Cancer] (IARC), which organizes the WHO classifications, started preparing for the fifth edition of the WHO classification. In past years, a major feature of preparing the revisions has been having a clinical advisory committee meeting in which pathologists, clinicians, and biologists gathered to discuss changes in the field and potential modifications to the classification.

Unfortunately, IARC rejected the use of a clinical advisory committee meeting for the fifth edition of the WHO, and the organizers felt that it was important to retain that program in preparing any changes of the classification. So, there was a clinical advisory committee meeting held at the University of Chicago and that led to the publication of the International Consensus Classification in June of 2022 in Blood. IARC proceeded with a separate structure and a separate group of authors and editors and published very recently online the fifth edition of the WHO classification. So today we're dealing with 2 different classifications, really for the first time since, I'd say, the 1980s when multiple classifications had been proposed.

During my remarks at the Pan Pacific meeting, I'll be presenting both classifications and discussing differences between them, where they differ and where they agree, and also, potential solutions for resolving these differences in a subsequent classification. I'd say that most of the major differences relate to B-cell lymphomas.

This includes follicular lymphoma, some of the other low grade small B-cell, neoplasms, diffuse large B-cell lymphoma, so-called double hit lymphomas, and finally, immunodeficiency disorders. My remarks will concentrate on follicular lymphoma and the aggressive B-cell lymphomas and a review of some of the small B-cell neoplasms.

I would say a general difference between the ICC and the WHO is that the ICC places of heavy emphasis on integration of histologic and molecular characteristics for classifying lymphomas. Whereas the WHO takes a more traditional morphologic approach and not all entities are defined by molecular phenotype. Some of the major changes introduced by the WHO was the elimination of B-cell prolymphocytic leukemia as an entity, and the elimination of hairy cell variant as an entity.

Both of these were combined under a new, what they call a placeholder, which is called I think splenic B-cell lymphoma with increased prolymphocytes. This category is a bit of a waste basket. The ICC retains both prolymphocytic leukemia and hairy cell variant, and tries to more accurately define these entities and apply criteria for differential diagnosis. Some of the same differences occur in follicular lymphoma, where some new entities are defined by the WHO.

There are also key differences in the classification of follicular lymphoma, with the ICC defining a new category of BCL2-negative follicular lymphoma that's generally associated with a strong expression of CD-23 and frequent a common genomic profile. Another difference between the ICC and the WHO is that the WHO eliminated one of the categories of double-hit lymphoma, which includes cases with rearrangements of MYC and BCL-6. The ICC retained this entity as a provisional category, recognizing that there is some heterogeneity within this category, and further studies are required.

Fortunately, I think both the ICC and the WHO take a very similar approach to the T-cell neoplasms. There are very minimal differences in terminology, but really no differences in recognition of the major entities. My remarks will mostly focus on differences in the B-cell lymphomas between the 2 classifications.

I will mention that there's an upcoming publication in JCO, which has been coauthored by participants in both the ICC and the WHO classification, also reviewing some of these differences and charting possible solutions for the future to reach a common understanding. We're all hoping that by the time the sixth edition comes around, there will be a unified classification used by all participants.

Thank you for your attention. I hope you found my brief remarks useful in your practice.

Source:

Jaffe E. Evolution in the Classification of Lymphoma: From WHO to ICC – where do we go from here. Presented at the 2024 Pan Pacific Lymphoma Conference. July 15–19, 2024; Lahaina, HI.