A BCL2 rearrangement test looks for a chromosome change that places the BCL2 gene under the control of a highly active partner, most often the immunoglobulin heavy-chain gene. The classic change is t(14;18)(q32;q21), written at the molecular level as an IGH::BCL2 fusion. It is strongly associated with conventional follicular lymphoma and is also important in aggressive B-cell lymphomas when it occurs together with a MYC rearrangement.
Testing is usually performed on lymph-node or other tumor tissue by fluorescence in situ hybridization, chromosome analysis, or next-generation sequencing. A positive BCL2 rearrangement supports a germinal-center B-cell process, but it does not diagnose lymphoma by itself. The same rearrangement can occur in different lymphoma settings, and rare low-level t(14;18)-positive cells can be found in healthy adults. Results must be combined with tissue architecture, cell appearance, immunohistochemistry, flow cytometry, MYC and BCL6 studies, and the clinical picture. BCL2 protein staining is not the same as a BCL2 gene rearrangement.
- A positive BCL2 rearrangement often supports conventional follicular lymphoma, especially when the tissue pattern and immunophenotype fit.
- Concurrent MYC and BCL2 rearrangements define an aggressive double-hit category in current lymphoma classifications.
- BCL2 protein overexpression does not prove a BCL2 rearrangement; FISH or another genomic method is needed.
- A negative result does not exclude follicular lymphoma, particularly in pediatric-type, grade 3B, or other BCL2-rearrangement-negative subtypes.
- The test usually uses biopsy tissue and requires no separate patient preparation beyond the biopsy procedure.
Table of Contents
- What a BCL2 Rearrangement Is
- When the Test Is Ordered
- How BCL2 Rearrangement Testing Works
- How to Read the Results
- BCL2 in Follicular Lymphoma
- BCL2 in Double-Hit Lymphoma
- How Results Affect Prognosis and Treatment
- Limitations and Questions to Ask
What a BCL2 Rearrangement Is
BCL2 encodes a protein that blocks programmed cell death, also called apoptosis. Normal B cells use carefully controlled survival signals while they mature in germinal centers of lymph nodes. A BCL2 rearrangement can move the gene next to an immunoglobulin enhancer, causing the cell to produce too much BCL2 protein. Abnormal B cells that should die may then survive long enough to collect additional changes.
The best-known rearrangement is t(14;18), in which material from chromosome 18 near BCL2 exchanges with chromosome 14 near IGH. The result is an IGH::BCL2 fusion. Less commonly, BCL2 joins an immunoglobulin light-chain gene or another partner. A laboratory may report “BCL2 rearrangement,” “IGH::BCL2 fusion,” or “t(14;18) detected.” These terms overlap but may reflect different test designs.
BCL2 rearrangement is a somatic event in lymphoma cells. It is not an inherited cancer mutation and does not mean relatives need germline testing. It can arise early in B-cell development, and tiny populations of t(14;18)-positive B cells are detectable in some healthy people, especially with increasing age. Those cells rarely become lymphoma. A molecular finding without a tissue lesion therefore cannot establish follicular lymphoma.
BCL2 rearrangement and BCL2 protein expression are related but not interchangeable. Immunohistochemistry stains the BCL2 protein in cells. Many lymphomas overexpress BCL2 without a rearrangement, and some tumors with unusual BCL2 variants may stain weakly with a particular antibody. A gene fusion test or FISH examines the genomic event directly.
The clinical meaning also depends on accompanying alterations. In a low-grade follicular lymphoma, BCL2 rearrangement is a characteristic diagnostic feature. In diffuse large B-cell lymphoma or another high-grade B-cell lymphoma, a BCL2 rearrangement becomes especially important when MYC is also rearranged. This combination changes classification and identifies a group with aggressive biology.
When the Test Is Ordered
A pathologist may order BCL2 rearrangement testing when biopsy findings suggest follicular lymphoma, diffuse large B-cell lymphoma, high-grade B-cell lymphoma, or transformation of an indolent lymphoma. Testing can be reflexive based on morphology and immunophenotype or specifically requested by the hematologist.
Common situations include:
- A nodular or follicular lymph-node pattern with CD10 and BCL6 expression
- Suspected follicular lymphoma with unusual BCL2 staining
- A large B-cell lymphoma with germinal-center phenotype
- Very high proliferation, blastoid or intermediate-sized cells, or starry-sky morphology
- Strong MYC and BCL2 protein coexpression
- Suspected transformation of follicular lymphoma to aggressive lymphoma
- A known MYC rearrangement that requires evaluation for BCL2 and BCL6 partners
- A limited biopsy in which classification remains uncertain
In conventional follicular lymphoma, the rearrangement is common but not universal. The pathologist may use it to support the diagnosis or distinguish follicular lymphoma from reactive follicular hyperplasia. Reactive germinal centers normally lack strong BCL2 protein expression, while many conventional follicular lymphomas express BCL2 because of t(14;18). Exceptions require full morphologic review.
In aggressive B-cell lymphoma, identifying a MYC rearrangement often triggers testing for BCL2. Current classifications define diffuse large B-cell lymphoma/high-grade B-cell lymphoma with MYC and BCL2 rearrangements as a distinct aggressive entity. BCL6 testing is frequently included because historical “double-hit” terminology also encompassed MYC/BCL6 and triple-hit cases, although modern WHO and ICC categories differ in how some combinations are grouped.
The test is not used to screen healthy people or to diagnose swollen lymph nodes without a biopsy. Enlarged nodes can result from infection, immune disease, or many cancers. Tissue architecture is critical, so a fine-needle aspiration alone may be insufficient for a new lymphoma diagnosis. Core or excisional biopsy is often preferred when feasible.
A broad lymphoma molecular panel may add mutation and copy-number data, but FISH remains a common, rapid method for MYC, BCL2, and BCL6 rearrangements. The methods complement rather than automatically replace each other.
How BCL2 Rearrangement Testing Works
Fluorescence in situ hybridization
FISH uses fluorescent DNA probes that bind near BCL2. A break-apart assay places differently colored probes on opposite sides of the usual breakpoint region. In normal cells, the signals sit together. When BCL2 is rearranged, they separate. A dual-fusion assay can specifically show IGH::BCL2 by demonstrating fusion of probes from chromosomes 14 and 18.
Break-apart FISH can detect BCL2 rearrangements with many partners, while an IGH/BCL2 dual-fusion probe answers a more specific question. Some laboratories use both when the first result is equivocal or when an uncommon pattern appears. A FISH test requires enough intact tumor nuclei and expert interpretation.
The report gives the percentage of abnormal nuclei and the laboratory cutoff. A result above the validated threshold is positive. Borderline percentages may prompt recounting, another probe, or a different tissue block. The percentage is not the percentage chance of treatment response.
Conventional chromosome analysis
Karyotyping can show t(14;18) and other chromosome changes in dividing cells. It provides a whole-chromosome view but requires viable cells and may miss abnormalities when tumor cells do not divide in culture. It is more commonly used in marrow and blood than in fixed lymph-node tissue.
Next-generation sequencing
DNA- or RNA-based sequencing can detect BCL2 rearrangements and identify the partner and breakpoint. RNA sequencing confirms that a fusion transcript is expressed. DNA panels vary in their coverage of large intronic breakpoint regions. A negative result on a panel that is not optimized for structural variants should not overrule convincing FISH or pathology.
Polymerase chain reaction
PCR assays can detect common IGH::BCL2 breakpoint regions and have been used for research or disease monitoring. They miss rearrangements outside the targeted breakpoints, so a negative PCR is less comprehensive than a validated break-apart or sequencing approach.
Specimen types and timing
Most tests use formalin-fixed paraffin-embedded tissue from a lymph node, extranodal mass, or bone marrow biopsy. Fresh tissue, cell suspensions, or cytology cell blocks may also work. Decalcified bone marrow can be challenging if harsh acid treatment damaged nucleic acids or nuclei.
No fasting is needed for the molecular test. Preparation relates to the biopsy or marrow procedure. Results may take several days to two weeks, depending on specimen quality, laboratory batching, and whether MYC and BCL6 are tested at the same time.
How to Read the Results
Positive BCL2 rearrangement
A positive result means enough analyzed tumor nuclei show a rearrangement involving BCL2. In a biopsy with typical low-grade follicular architecture, germinal-center markers, and appropriate morphology, it strongly supports conventional follicular lymphoma. In an aggressive lymphoma, the result must be paired with MYC status.
The report may state the partner, such as IGH, or only that BCL2 is rearranged. It may also describe extra signals, copy-number changes, or an atypical pattern. A pathologist should determine whether those patterns meet criteria for a true rearrangement.
A positive result does not show stage. Stage requires imaging, physical examination, marrow assessment when indicated, and clinical evaluation. It also does not determine whether immediate treatment is necessary. Many people with low-tumor-burden follicular lymphoma can be observed despite a positive BCL2 result.
Negative BCL2 rearrangement
A negative result means no rearrangement was detected above the assay cutoff in the tested sample. It does not exclude follicular lymphoma. BCL2-rearrangement-negative follicular lymphomas include biologically distinct groups, such as pediatric-type follicular lymphoma, diffuse follicular lymphoma with certain 1p36 changes, and some higher-grade cases.
A negative result may also reflect low tumor content, poor nuclei, a cryptic breakpoint outside probe coverage, or sampling of an uninvolved area. The report should state whether the specimen was adequate.
Equivocal or atypical
An equivocal result occurs when the abnormal percentage is near the cutoff or signal patterns are technically difficult. An atypical result may show loss or gain of one probe, multiple copies, or a complex pattern. These findings can arise from true complex rearrangements, aneuploidy, truncation artifacts, or poor tissue preservation.
The laboratory may repeat scoring, test another block, use an IGH/BCL2 fusion probe, or perform sequencing. Clinical decisions should not rely on an unresolved borderline result when more tissue or another method is available.
BCL2 protein positive but rearrangement negative
This combination is common in aggressive lymphomas. BCL2 protein can be increased through amplification, transcriptional activation, or other mechanisms. The tumor may be a “double-expressor” lymphoma if MYC protein is also high, but double expression is not the same as a double-hit rearrangement. Immunohistochemistry uses protein-percentage thresholds; FISH demonstrates gene rearrangements.
BCL2 in Follicular Lymphoma
Conventional follicular lymphoma arises from germinal-center B cells and usually has a follicular or nodular growth pattern. Most low-grade cases carry t(14;18) and express CD20, CD10, BCL6, and BCL2. The rearrangement is an early event, but additional mutations involving epigenetic regulators and immune interactions are needed for overt lymphoma.
A diagnosis requires more than the fusion. Pathologists assess follicle shape, mantle zones, tingible-body macrophages, cytology, grade, and distribution. Reactive follicles can contain rare t(14;18)-positive cells without lymphoma. Conversely, some true follicular lymphomas lack BCL2 rearrangement.
Follicular lymphoma grading is based on the number and pattern of large centroblasts. Grades 1, 2, and 3A generally remain within the conventional indolent spectrum, although clinical behavior varies. Grade 3B has sheets of centroblasts and differs biologically; BCL2 rearrangement is less common, while BCL6 rearrangement may be more frequent.
Several special entities are usually BCL2-rearrangement negative:
- Pediatric-type follicular lymphoma, often localized and highly curable
- Primary cutaneous follicle-center lymphoma, which usually lacks t(14;18)
- Duodenal-type follicular lymphoma, which often carries BCL2 rearrangement but has a distinct, indolent presentation
- BCL2-rearrangement-negative CD23-positive follicle-center lymphoma, a provisional group in the ICC
This diversity explains why a positive result is supportive rather than universally required. The final pathology wording should state the recognized entity, not merely “BCL2 positive.”
BCL2 rearrangement is not generally used as a stand-alone marker to monitor routine follicular lymphoma in blood. Imaging, examination, symptoms, blood counts, and sometimes biopsy guide follow-up. Molecular detection can persist at low levels without clinical disease and may not correlate directly with tumor burden.
BCL2 in Double-Hit Lymphoma
“Double-hit lymphoma” commonly refers to an aggressive B-cell lymphoma with rearrangements of both MYC and BCL2. MYC drives cell growth and proliferation, while BCL2 blocks cell death. Together they create a biologically aggressive combination. A third BCL6 rearrangement may also be present, producing a so-called triple-hit pattern.
Current WHO terminology uses diffuse large B-cell lymphoma/high-grade B-cell lymphoma with MYC and BCL2 rearrangements. The ICC similarly recognizes a high-grade B-cell lymphoma category with MYC and BCL2 rearrangements, including some triple-hit cases. MYC/BCL6-only rearranged tumors are handled differently between classification systems and should not automatically be called the same entity as MYC/BCL2 double-hit lymphoma.
Double-hit status requires genomic evidence. High MYC and BCL2 protein expression by immunohistochemistry defines a double-expressor phenotype, not a double-hit genotype. Double-expressor lymphoma is more common and has heterogeneous biology. It may carry worse risk than tumors without coexpression, but it does not substitute for FISH.
Aggressive lymphomas considered for double-hit testing often show a germinal-center B-cell phenotype, high Ki-67 proliferation, extranodal disease, marrow involvement, or elevated lactate dehydrogenase. None of these features is sufficiently sensitive to decide who has the rearrangements. Many centers therefore use broad FISH strategies for newly diagnosed large B-cell lymphoma, while others apply an immunophenotypic screening algorithm.
Transformation can occur when an existing follicular lymphoma acquires MYC rearrangement or other changes and becomes a high-grade lymphoma. Comparing current and prior tissue can show whether the aggressive tumor evolved from the earlier clone. The distinction affects the clinical history but does not reduce the urgency of treating the high-grade disease.
How Results Affect Prognosis and Treatment
In follicular lymphoma, BCL2 rearrangement mainly supports diagnosis and biology. It does not by itself determine when treatment starts. Decisions use symptoms, threatened organs, cytopenias, bulky disease, progression, stage, and patient preference. Options can include observation, radiation for localized disease, anti-CD20 therapy, immunochemotherapy, targeted agents, bispecific antibodies, cellular therapy, and clinical trials depending on setting.
In MYC/BCL2 double-hit lymphoma, the rearrangement changes classification and identifies a group at increased risk of treatment failure and central nervous system involvement compared with many ordinary diffuse large B-cell lymphomas. Treatment often uses an intensive multiagent regimen when the patient can tolerate it, but the best approach remains under study and depends on age, fitness, stage, organ function, and local guidelines.
The molecular result is one part of prognostic assessment. The International Prognostic Index uses age, stage, lactate dehydrogenase, performance status, and extranodal sites. PET/CT response, marrow findings, circulating tumor DNA research assays, and treatment tolerance add information over time.
BCL2 is also a therapeutic protein target. Venetoclax inhibits BCL2 and is highly effective in several leukemias, but its role in most follicular and large B-cell lymphomas is less established and often investigational or combination-based. A BCL2 rearrangement does not automatically mean venetoclax is approved or will work. Protein dependence, co-mutations, disease type, and trial evidence matter.
A pathology report should reach the treating hematologist before finalizing first-line therapy for aggressive lymphoma. Delayed FISH results can lead to a provisional plan that needs adjustment. When tissue is limited, prioritizing MYC, BCL2, and BCL6 studies may prevent an incomplete classification.
Limitations and Questions to Ask
The test examines only the sampled tissue. Lymphomas can be heterogeneous, and a small core may miss a transformed area. Formalin damage, decalcification, low tumor content, overlapping nuclei, and uncommon breakpoints can cause false-negative or indeterminate results.
FISH does not show the full genomic context. It may detect a rearrangement without identifying the partner, orientation, or whether the fusion is expressed. Sequencing may clarify those details but can miss structural variants if panel design is limited.
Useful questions include:
- Was the result from break-apart FISH, IGH/BCL2 fusion FISH, karyotype, or sequencing?
- Did the specimen contain enough lymphoma cells?
- Was MYC tested, and was BCL6 also evaluated?
- Is this follicular lymphoma, transformed lymphoma, diffuse large B-cell lymphoma, or high-grade B-cell lymphoma?
- Is the tumor double-hit, triple-hit, double-expressor, or none of these?
- Does the result change the recommended treatment regimen or CNS evaluation?
- Should another biopsy be considered if clinical behavior and pathology do not match?
- Is there enough tissue for additional molecular testing or a clinical trial?
Urgent care is appropriate for rapidly enlarging masses, breathing or swallowing difficulty, new weakness or numbness, severe abdominal pain, confusion, or signs of tumor lysis after therapy begins. A BCL2 result itself is not an emergency, but the aggressive diseases it can help identify may require prompt treatment.
The most accurate interpretation is a complete integrated diagnosis. The rearrangement, morphology, immunophenotype, and clinical findings should appear together in the final pathology report so that one isolated biomarker is not mistaken for the entire disease.
Why the final integrated report matters
A preliminary FISH line can be misleading when separated from the completed pathology interpretation. For example, a BCL2 rearrangement in a small B-cell lymphoma may fit follicular lymphoma, while the same finding in a blastoid large-cell process requires MYC testing and a different diagnostic framework. The final report should state the tumor entity, grade or cytology when applicable, protein profile, rearrangement results, and any unresolved limitations.
Clinicians should also confirm that MYC and BCL2 refer to gene rearrangements rather than protein stains. Phrases such as “MYC positive” and “BCL2 positive” can describe immunohistochemistry, whereas “MYC rearranged” and “BCL2 rearranged” describe genomic findings. Confusing these terms can change risk discussions and treatment plans.
When an outside biopsy is transferred to a tertiary center, review of slides, blocks, and original FISH images may be worthwhile before intensive therapy. Repeat testing is most useful when the initial specimen was scant, the result was borderline, or classification criteria have changed. It is not automatically required when a validated study and expert review are concordant, the tissue is representative, and the clinical behavior fits the integrated diagnosis without unexplained discrepancies between pathology, imaging, laboratory findings, symptoms, and the observed tempo of disease progression overall.
References
- The International Consensus Classification of Mature Lymphoid Neoplasms: a report from the Clinical Advisory Committee 2022 (Position Statement)
- Follicular Lymphoma in the 5th Edition of the WHO-Classification of Haematolymphoid Neoplasms—Updated Classification and New Biological Data 2023 (Review)
- The pathobiology of follicular lymphoma 2023 (Review)
- B- and T-/NK-Cell Lymphomas in the 2022 International Consensus Classification of Mature Lymphoid Neoplasms and Comparison with the WHO Fifth Edition 2024 (Review)
- The Management of Newly-Diagnosed Large B-cell Lymphoma: A British Society for Haematology Guideline 2024 (Guideline)
- Clinicopathological characteristics, genetic aberrations and prognostic factors of high-grade B-cell lymphoma with MYC and BCL2 and/or BCL6 rearrangements 2025
Disclaimer
This article is educational and does not replace interpretation by a hematopathologist or treatment advice from a hematologist-oncologist. BCL2 rearrangement results must be combined with tissue morphology, immunophenotype, MYC and BCL6 findings, specimen quality, stage, and the patient’s health. Seek urgent care for breathing difficulty, neurologic symptoms, severe pain, or rapidly worsening swelling.
