# Splenic marginal zone lymphoma
**Splenic marginal zone lymphoma** (SMZL) is a rare, typically indolent (slow-growing) B-cell non-[Hodgkin lymphoma](https://www.edgepedia.org/hodgkin-lymphoma) that arises in the [marginal zone of the spleen](https://www.edgepedia.org/marginal-zone-of-the-spleen) and usually also involves the bone marrow and, frequently, the blood.[1](https://pubmed.ncbi.nlm.nih.gov/26989207/) It is one of three types of marginal zone lymphoma distinguished by site of origin, the others arising in lymph nodes or in extranodal lymphoid tissue rich in B cells.[2](https://www.cancer.gov/publications/dictionaries/cancer-terms/def/marginal-zone-lymphoma) SMZL constitutes fewer than 2% of lymphoid neoplasms.[3](https://pmc.ncbi.nlm.nih.gov/articles/PMC11390296/)
| Key fact | Detail |
|---|---|
| Definition | Indolent B-cell non-Hodgkin lymphoma of the splenic marginal zone, involving spleen, bone marrow, and frequently the blood[1](https://pubmed.ncbi.nlm.nih.gov/26989207/) • [2](https://www.cancer.gov/publications/dictionaries/cancer-terms/def/marginal-zone-lymphoma) |
| Frequency | Fewer than 2% of lymphoid neoplasms[3](https://pmc.ncbi.nlm.nih.gov/articles/PMC11390296/) |
| Course | Median survival approximately 10 years, but nearly 30% of patients have a poor outcome[1](https://pubmed.ncbi.nlm.nih.gov/26989207/) |
| Transformation | 5–15% of cases transform to large cell lymphoma, with especially poor prognosis[3](https://pmc.ncbi.nlm.nih.gov/articles/PMC11390296/) |
| Characteristic genetics | 7q deletion in ~30%; KLF2 mutations in 20–42%; NOTCH2 mutations in 6.5–25%[4](https://ashpublications.org/blood/article/127/17/2072/34950/Splenic-marginal-zone-lymphoma-from-genetics-to) • [5](https://www.sciencedirect.com/science/article/pii/S2214663615000139) |
| Infection link | In some geographic areas a subset of patients has hepatitis C virus infection, and antiviral eradication can treat the lymphoma[1](https://pubmed.ncbi.nlm.nih.gov/26989207/) |
| First-line options | Watch-and-wait for asymptomatic patients; splenectomy, rituximab alone, rituximab plus chemotherapy, or chemotherapy for symptomatic disease[6](https://www.sciencedirect.com/science/article/pii/S0923753419354651) |
| Evidence base | No randomized trials reported; few prospective trials available[1](https://pubmed.ncbi.nlm.nih.gov/26989207/) |
## Classification
The International Consensus Classification of Mature Lymphoid Neoplasms retains the definition of SMZL used in the 4th edition of the WHO classification: a mature B-cell neoplasm primarily involving the spleen, grouped alongside hairy cell leukemia, [hairy cell leukemia variant](https://www.edgepedia.org/hairy-cell-leukemia-variant), [splenic diffuse red pulp lymphoma](https://www.edgepedia.org/splenic-diffuse-red-pulp-lymphoma), and splenic [B-cell lymphoma](https://www.edgepedia.org/b-cell-lymphoma)/leukemia unclassifiable.[3](https://pmc.ncbi.nlm.nih.gov/articles/PMC11390296/) Marginal zone lymphomas as a group are indolent B-cell non-Hodgkin lymphomas beginning in the marginal zones of lymph tissue, subdivided by whether they form in the spleen, the lymph nodes, or other B-cell-rich lymphoid tissue.[2](https://www.cancer.gov/publications/dictionaries/cancer-terms/def/marginal-zone-lymphoma)
## Pathogenesis and genetics
**Antigen drive.** The highly restricted immunoglobulin gene repertoire of SMZL, including a stereotyped B-cell receptor configuration in about 10% of cases and selective usage of the Ig heavy chain variable IGHV1-2*04 allele in about 30%, points to antigen or superantigen stimulation in lymphomagenesis.[4](https://ashpublications.org/blood/article/127/17/2072/34950/Splenic-marginal-zone-lymphoma-from-genetics-to) About 90% of cases carry somatic mutations in their rearranged immunoglobulin genes, at remarkably variable degrees, suggesting multiple cells of origin within the heterogeneous B cells of the splenic marginal zone.[5](https://www.sciencedirect.com/science/article/pii/S2214663615000139)
**Recurrent lesions.** Approximately 30% of SMZL show hemizygous deletion of the long arm of chromosome 7, a lesion seen frequently in splenic B-cell lymphoma/leukemia unclassifiable but rarely in other lymphoma subtypes; the targeted gene or genes remain unidentified.[4](https://ashpublications.org/blood/article/127/17/2072/34950/Splenic-marginal-zone-lymphoma-from-genetics-to) Recurrent mutations target the pathways that govern development of splenic marginal zone B cells: KLF2 in 20–42% of cases, NOTCH2 in 6.5–25%, NF-κB pathway genes (CARD11 about 7%, [IKBKB](https://www.edgepedia.org/ikbkb) about 7%, TNFAIP3 7–13%, TRAF3 5%, BIRC3 6.3%), and the [Toll-like receptor](https://www.edgepedia.org/toll-like-receptor) pathway gene MYD88 in 5–13%.[5](https://www.sciencedirect.com/science/article/pii/S2214663615000139) A whole-exome sequencing study of 96 SMZLs found KLF2 mutation in 42% but rarely in other B-cell lymphomas.[7](https://pubmed.ncbi.nlm.nih.gov/25428260/)
**Mechanism.** KLF2 is a zinc-finger transcription factor that normally suppresses NF-κB induction by upstream signaling, including the B-cell receptor and Toll-like receptor pathways; most KLF2 mutations disrupt its nuclear localization signal or DNA-interacting codons, and the resulting deregulation consistently activates NF-κB.[4](https://ashpublications.org/blood/article/127/17/2072/34950/Splenic-marginal-zone-lymphoma-from-genetics-to) NOTCH2 upregulation or KLF2 inactivation alone is not sufficient for malignant transformation: transgenic mice engineered to overexpress NOTCH2, or lacking KLF2 in mature B cells, show expansion of the marginal zone at the expense of the follicular compartment but do not develop lymphoma.[4](https://ashpublications.org/blood/article/127/17/2072/34950/Splenic-marginal-zone-lymphoma-from-genetics-to) IGHV1-2*04 usage, NOTCH2 and KLF2 mutations, KLF4 aberrant methylation, and 7q deletion co-occur in a disease subset, suggesting cooperation among genetic and epigenetic abnormalities and B-cell receptor configuration.[4](https://ashpublications.org/blood/article/127/17/2072/34950/Splenic-marginal-zone-lymphoma-from-genetics-to)
## Diagnosis
Diagnosis requires either spleen histology or, alternatively, documentation of typical cell morphology and immunophenotype on blood cells together with detection of intrasinusoidal infiltration by CD20-positive cells in the bone marrow.[1](https://pubmed.ncbi.nlm.nih.gov/26989207/) Among mature B-cell tumors, deletion of 7q and NOTCH2 mutations are almost specific for SMZL and serve as diagnostic biomarkers; NOTCH2 mutations carry positive predictive value for SMZL specification.[1](https://pubmed.ncbi.nlm.nih.gov/26989207/) • [4](https://ashpublications.org/blood/article/127/17/2072/34950/Splenic-marginal-zone-lymphoma-from-genetics-to) KLF2 mutations are not diagnostically specific because they also occur in other indolent B-cell tumors, but they are relatively sensitive and specific markers of a splenic origin compared with nodal and extranodal marginal zone lymphomas.[4](https://ashpublications.org/blood/article/127/17/2072/34950/Splenic-marginal-zone-lymphoma-from-genetics-to) • [8](https://pmc.ncbi.nlm.nih.gov/articles/PMC8482189/) NCCN guidance notes that NOTCH2 and KLF2 mutation status may help differentiate SMZL from other B-cell lymphoma subtypes.[9](https://www.gluetacs.com/wp-content/themes/gluetacs/pdf/NCCN%E4%B8%B4%E5%BA%8A%E5%AE%9E%E8%B7%B5%E6%8C%87%E5%8D%97%EF%BC%9AB%E7%BB%86%E8%83%9E%E6%B7%8B%E5%B7%B4%E7%98%A4%EF%BC%882024.V1%EF%BC%89%20NCCN%20Guidelines%20B-Cell%20Lymphomas%20Myeloma%20Version%202.2024.pdf)
## Prognosis
The majority of SMZLs follow an indolent course with a median survival of approximately 10 years, but nearly 30% of patients experience a poor outcome.[1](https://pubmed.ncbi.nlm.nih.gov/26989207/) [Prognosis](https://www.edgepedia.org/prognosis) is especially poor for the 5–15% of cases that transform to a large cell lymphoma.[3](https://pmc.ncbi.nlm.nih.gov/articles/PMC11390296/) Both NOTCH2 and KLF2 mutations mark cases with inferior outcome.[4](https://ashpublications.org/blood/article/127/17/2072/34950/Splenic-marginal-zone-lymphoma-from-genetics-to) In a cohort of 64 patients treated in the rituximab era, median overall survival was 156.3 months and median progression-free survival was 52.9 months, with baseline hemoglobin below 12 g/dl associated with inferior overall survival.[10](https://pubmed.ncbi.nlm.nih.gov/28105889/)
## Treatment
**Watch-and-wait.** For asymptomatic patients, an active surveillance policy is recommended, with follow-up evaluation every 3 to 6 months including physical examination, abdominal ultrasound, blood count, and biochemistry.[6](https://www.sciencedirect.com/science/article/pii/S0923753419354651)
**Hepatitis C.** In patients with concomitant chronic hepatitis C virus infection who do not immediately need conventional treatment, antiviral therapy should be considered; in some geographic areas virus eradication is an effective lymphoma treatment.[6](https://www.sciencedirect.com/science/article/pii/S0923753419354651) • [1](https://pubmed.ncbi.nlm.nih.gov/26989207/)
**Starting treatment.** The main criteria for initiating treatment are progressive or symptomatic splenomegaly and/or progressive cytopaenias, defined as hemoglobin below 10 g/dl, platelets below 80,000/μl, or neutrophils below 1,000/μl; associated autoimmune disorders such as autoimmune hemolytic anemia or immune thrombocytopenia should be specifically treated.[6](https://www.sciencedirect.com/science/article/pii/S0923753419354651)
**Options and comparison.** Recognized therapeutic options are splenectomy, chemotherapy, rituximab alone, or rituximab plus chemotherapy.[6](https://www.sciencedirect.com/science/article/pii/S0923753419354651) In a series of 85 patients, rituximab monotherapy (375 mg/m² weekly for 6 weeks, then maintenance every 2 months for 1–2 years) produced an overall response rate of 95% with 45% complete responses, and 5-year overall survival of 92% versus 77% after splenectomy and 5-year progression-free survival of 73% versus 58%; maintenance therapy lengthened remission, with 5-year progression-free survival of 84% with maintenance versus 36% without.[11](https://pmc.ncbi.nlm.nih.gov/articles/PMC3579603/) A retrospective study of 43 patients found complete response in 79% after rituximab versus 30% after chemotherapy without rituximab, with less toxicity for monotherapy, and 3-year disease-free survival of 79% after rituximab versus 29% after splenectomy alone.[12](https://pubmed.ncbi.nlm.nih.gov/23016878/) In a SEER-Medicare analysis of patients with a median age of 77 years, lymphoma-related death at 3 years was similar after systemic therapy (19.6%) and splenectomy (17.3%), 90-day mortality after splenectomy was 7.1%, and single-agent rituximab was suggested to offer the most favorable risk/benefit ratio in this population.[13](https://pubmed.ncbi.nlm.nih.gov/24057925/) [Splenectomy](https://www.edgepedia.org/splenectomy) retains a role for nonresponders and as a combined diagnostic and therapeutic procedure in disease confined to the spleen.[14](https://bmccancer.biomedcentral.com/track/pdf/10.1186/s12885-020-07204-6)
No randomized trials have been reported for SMZL, and few prospective trials are available.[1](https://pubmed.ncbi.nlm.nih.gov/26989207/)
## References
1. [Arcaini L, Rossi D, Paulli M (2016). Splenic marginal zone lymphoma: from genetics to management. Blood.](https://pubmed.ncbi.nlm.nih.gov/26989207/)
2. [Definition of marginal zone lymphoma, NCI Dictionary of Cancer Terms](https://www.cancer.gov/publications/dictionaries/cancer-terms/def/marginal-zone-lymphoma)
3. [The genomic and molecular landscape of splenic marginal zone lymphoma, biological and clinical implications, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC11390296/)
4. [Splenic marginal zone lymphoma: from genetics to management, Blood (full text)](https://ashpublications.org/blood/article/127/17/2072/34950/Splenic-marginal-zone-lymphoma-from-genetics-to)
5. [Pathogenesis of splenic marginal zone lymphoma, ScienceDirect](https://www.sciencedirect.com/science/article/pii/S2214663615000139)
6. [Marginal zone lymphomas: ESMO Clinical Practice Guidelines, ScienceDirect](https://www.sciencedirect.com/science/article/pii/S0923753419354651)
7. [KLF2 mutation is the most frequent somatic change in splenic marginal zone lymphoma, PubMed](https://pubmed.ncbi.nlm.nih.gov/25428260/)
8. [New Insights into the Biology and Diagnosis of Splenic Marginal Zone Lymphomas, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC8482189/)
9. [NCCN Guidelines Version 2.2024, B-Cell Lymphomas](https://www.gluetacs.com/wp-content/themes/gluetacs/pdf/NCCN%E4%B8%B4%E5%BA%8A%E5%AE%9E%E8%B7%B5%E6%8C%87%E5%8D%97%EF%BC%9AB%E7%BB%86%E8%83%9E%E6%B7%8B%E5%B7%B4%E7%98%A4%EF%BC%882024.V1%EF%BC%89%20NCCN%20Guidelines%20B-Cell%20Lymphomas%20Myeloma%20Version%202.2024.pdf)
10. [Splenic marginal zone lymphoma: excellent outcomes in 64 patients treated in the rituximab era, PubMed](https://pubmed.ncbi.nlm.nih.gov/28105889/)
11. [Treatment of SMZL With Rituximab Monotherapy: Progress Report and Comparison With Splenectomy, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC3579603/)
12. [Rituximab, used alone or in combination, is superior to other treatment modalities in SMZL, PubMed](https://pubmed.ncbi.nlm.nih.gov/23016878/)
13. [Comparative outcomes of rituximab-based systemic therapy and splenectomy in SMZL, PubMed](https://pubmed.ncbi.nlm.nih.gov/24057925/)
14. [Risk adapted approach: How to treat SMZL in resource-poor settings, BMC Cancer](https://bmccancer.biomedcentral.com/track/pdf/10.1186/s12885-020-07204-6)
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*Topic: Encyclopedia › Life and health › Human health and medicine › Diseases and injuries › Cardiovascular and blood conditions › Blood disorders (hematologic conditions) › Lymphomas › B-cell non-Hodgkin lymphomas › Hairy cell leukemia and other splenic B-cell lymphomas/leukemias*
*Initially written Sep 17, 2026 · Reviewed: Oct 21, 2026 · Edited: Oct 15, 2026; Oct 21, 2026 · Last review: Oct 21, 2026*
*Copyright 2026 EdgeChat AI, a subsidiary of Biostate AI.*
License: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license