Hodgkin lymphoma and primary mediastinal B-cell lymphoma
Panelist Lisa G. Roth, MD, of Weill Cornell Medicine, New York, reviewed the genomic landscape of Hodgkin lymphoma (HL) and primary mediastinal B-cell lymphoma (PMBCL).
Dr. Roth explained that both HL and PMBCL are derived from thymic B cells, predominantly affect the mediastinum, and are CD30-positive lymphomas. Both are characterized by upregulation of JAK/STAT and NF-kappaB as well as overexpression of PD-L1.
Dr. Roth noted that HL is challenging to sequence by standard methods because Reed Sternberg (HRS) cells represent less than 1% of the cellular infiltrate. Recurrently mutated genes in HL cluster by histologic subtype.
Whole-exome sequencing of HRS cells show loss of beta-2 microglobulin and MHC-1 expression, HLA-B, NF-kappaB signaling, and JAK-STAT signaling, according to data published in Blood Advances in 2019.
Dr. Roth’s lab performed immunohistochemistry on tissue microarrays in 145 cases of HL (unpublished data). Results showed that loss of beta-2 microglobulin is more common in younger HL patients. For other alterations, there were too few cases to know.
Dr. Roth’s lab is a member of a pediatric/AYA HL sequencing multi-institutional consortium that has been able to extract DNA and RNA from samples submitted for whole-exome sequencing. The consortium’s goal is to shed light on implications of other genomic alterations that may differ by age in HL patients.
Dr. Roth cited research showing that PMBCL shares molecular alterations similar to those of HL. Alterations in PMBCL suggest dysregulated cellular signaling and immune evasion mechanisms (e.g., deletions in MHC type 1 and 2, beta-2 microglobulin, JAK-STAT, and NF-kappaB mutations) that provide opportunities to study novel agents, according to data published in Blood in 2019.
By early 2021, the S1826 and ANHL1931 studies, which have no age restriction, will be available to AYA lymphoma patients with HL and PMBCL, respectively, Dr. Roth said.
Follicular lymphoma: Clinical features by age
Panelist Abner Louissaint Jr, MD, PhD, of Massachusetts General Hospital in Boston, discussed age-related differences in follicular lymphoma (FL).
He noted that FL typically presents at an advanced stage, with low- or high-grade histology. It is increasingly common in adults in their 50s and 60s, representing 20% of all lymphomas. FL is rare in children and AYAs.
Dr. Louissaint explained that the typical flow cytometric findings in FL are BCL2 translocations, occurring in up to 85%-90% of low-grade and 50% of high-grade cases. The t(14;18)(q32;q21) translocation juxtaposes BCL2 on 18q21 to regulatory sequences and enhances the expression of elements of the Ig heavy chain.
Malignant cells in FL patients express CD20, CD10, CD21, and BCL2 (in contrast to normal germinal centers) and overexpress BCL6 (in contrast to normal follicles), Dr. Louissaint noted. He said the Ki-67 proliferative index of the malignant cells is typically low.
Pediatric-type FL is rare, but case series show clinical, pathologic, and molecular features that are distinctive from adult FL, Dr. Louissaint explained.
He then discussed the features of pediatric-type FL in multiple domains. In the clinical domain, there is a male predilection, and stage tends to be low. There is frequent involvement of nodes of the head and neck region and rare involvement of internal lymph node chains.
Pathologically, the malignant cells appear high grade, with architectural effacement, expansile follicular pattern, large lymphocyte size, and an elevated proliferation index. In contrast to adult FL, malignant cells in pediatric-type FL lack aberrant BCL2 expression.
Most importantly, for pediatric-type FL, the prognosis is excellent with durable remissions after surgical excision, Dr. Louissaint said.