Double-hit and triple-hit lymphomas are subtypes of Diffuse Large B-cell Lymphoma (DLBCL) characterized by specific genetic rearrangements that make the disease highly aggressive and difficult to treat.
In the 2022 WHO revision of lymphoma classification, these are officially designated as “high-grade B-cell lymphomas (HGBLs) with MYC and BCL2 and/or BCL6 rearrangements”.
I. Definitions
- Double-Hit Lymphoma: Occurs when a patient’s lymphoma cells have a rearrangement of the MYC gene in addition to a rearrangement of either the BCL2 or BCL6 gene.
- Triple-Hit Lymphoma: Occurs when rearrangements of all three genes—MYC, BCL2, and BCL6—are present simultaneously.
II. Biological Mechanism and Pathophysiology
The combination of these specific genetic hits provides a significant survival advantage to malignant cells:
- MYC Rearrangement: Acts as an accelerator by promoting rapid tumor proliferation.
- BCL2 Protein Expression: Acts as a brake against cell death by inhibiting apoptosis.
III. Clinical Impact for the Oncology Pharmacist
For BCOP preparation, it is critical to understand the clinical implications of these “hits”:
- Aggressive Behavior: These lymphomas exhibit highly aggressive clinical behavior and pathophysiologic features that overlap with Burkitt lymphoma.
- CNS Risk: There is a reported increased incidence of central nervous system (CNS) involvement.
- Poor Outcomes: Patients typically have very poor clinical outcomes and significantly lower progression-free and overall survival rates compared to other DLBCL subtypes, even when treated with rituximab-containing chemoimmunotherapy or intensive therapy followed by stem cell transplantation.
- Standard Therapy Limitation: The standard R-CHOP regimen has been associated with inferior outcomes in this population. While a standard of care is not yet established, more intensive regimens like DA-R-EPOCH are often explored as potential frontline options.
IV. Distinction from “Double Expressor” Lymphoma
It is important to distinguish these genetic “hits” from Double Expressor Lymphoma (DEL). DEL refers to the co-expression of MYC and BCL2 proteins without the underlying genetic rearrangements. While DEL is not considered a unique category like HGBL, it is recognized as a new adverse prognostic indicator.