Non-Hodgkin lymphoma (NHL) represents a heterogeneous group of lymphoid malignancies arising from B cells, T cells, or natural killer cells and accounts for a significant proportion of hematological cancers worldwide. The global incidence of NHL has shown a gradual increase over recent decades, with considerable geographic variation influenced by environmental, genetic, and demographic factors [1, 2]. In India, mature B-cell lymphomas constitute the majority of NHL cases, among which indolent small B-cell lymphomas form an important subgroup characterized by relatively slow disease progression and prolonged survival [3, 4].

Indolent small B-cell lymphomas include entities such as marginal zone lymphoma, lymphoplasmacytic lymphoma, and other low-grade B-cell neoplasms. These lymphomas frequently exhibit overlapping morphological and immunophenotypic features, which may create diagnostic challenges in routine hematopathology practice. Contemporary classification systems, including the recent World Health Organization classification of hematolymphoid tumors and the International Consensus Classification, recommend an integrated diagnostic approach combining histopathology, immunophenotyping, molecular findings, and clinical correlation to achieve accurate classification [5, 6].

Despite advances in diagnostic techniques, atypical clinical presentations—such as predominant bone marrow involvement, monoclonal gammopathy, or aberrant antigen expression—may complicate the distinction between various indolent small B-cell lymphoma subtypes. Such diagnostic uncertainty may influence prognostic assessment and therapeutic decision-making. Furthermore, limited data are available from regional tertiary care centers regarding the clinicopathological spectrum and diagnostic challenges of indolent small B-cell lymphomas in the Indian population.

Therefore, the present study was undertaken to evaluate the clinicopathological characteristics and diagnostic challenges associated with indolent small B-cell lymphomas in adult patients at a tertiary care center. By correlating clinical presentation, morphology, immunophenotypic findings, and cytogenetic features, this study aims to highlight potential diagnostic pitfalls and emphasize the importance of an integrated approach for accurate classification.

MATERIALS AND METHODS

Study Design and Setting

The present study was designed as a retrospective observational analysis conducted in the Department of Pathology at a tertiary care teaching hospital. The study period extended from January 2022 to November 2025. Clinical records, laboratory data, radiological findings, histopathology reports, immunohistochemistry results, cytogenetic information, and follow-up details were reviewed from institutional archives and electronic medical records.

Study Population

Adult patients diagnosed with indolent small B-cell non-Hodgkin lymphoma during the study period were included in the analysis. Particular attention was given to cases demonstrating atypical clinical presentations or overlapping morphological and immunophenotypic features that could pose diagnostic challenges.

Inclusion Criteria

Patients were included in the study if they fulfilled the following criteria:

1. Age 18 years or older.
2. Histopathologically confirmed diagnosis of indolent small B-cell lymphoma.
3. Availability of adequate tissue material and immunohistochemical evaluation for definitive diagnosis.

Exclusion Criteria

Cases were excluded if clinical records were incomplete, tissue samples were inadequate for proper histopathological assessment, or if patients had previously been diagnosed with aggressive lymphoma or had received prior lymphoma-specific therapy.

Histopathological Evaluation

All tissue specimens were fixed in formalin and processed using routine paraffin-embedding techniques. Sections were stained with hematoxylin and eosin and carefully examined by experienced pathologists. Morphological evaluation included assessment of lymphoid cell morphology, architectural patterns, and the presence of bone marrow infiltration when applicable.

Immunohistochemical Analysis

Immunohistochemical staining was performed using a panel of antibodies commonly used in the evaluation of B-cell lymphomas, including CD20, CD5, CD23, CD10, Cyclin D1, BCL2, and BCL6. Bone marrow biopsy specimens were also assessed to determine the pattern and extent of lymphomatous

Diagnostic Criteria

Final classification of lymphoma subtypes was established according to the latest international guidelines for hematolymphoid neoplasms, incorporating morphological findings, immunophenotypic features, cytogenetic results, and relevant clinical information.

Ethical Considerations

The study was conducted in accordance with institutional ethical standards. The study protocol was approved by the Institutional Ethics Committee of Bhagyoday Medical College, Kadi, Gujarat, India (Approval No: BMC/IEC/2025/Path/07).

RESULTS

A total of three adult male patients diagnosed with indolent small B-cell lymphoma were included in the study. The age of the patients ranged from 43 to 70 years, with a median age of 69 years. Clinical presentation varied among the patients and included unexplained anemia, peripheral neuropathy, and localized cervical lymphadenopathy. Constitutional (B) symptoms were absent in all cases. Bone marrow involvement was identified in all three patients at the time of diagnosis. The clinical and laboratory characteristics of the patients are summarized in Table 1.

Table 1: Clinical and Laboratory Profile of Patients

The histopathological and immunophenotypic findings are presented in Table 2. Morphological patterns included interstitial marrow infiltration, paratrabecular infiltration, and nodal architectural effacement (Figure 1, 2). All cases demonstrated CD20 positivity, confirming B-cell lineage. CD5 expression was variable, while CD23, CD10, and Cyclin D1 were negative in most cases. Based on these findings, cases were interpreted as probable marginal zone lymphoma, lymphoplasmacytic overlap lymphoma, and low-grade B-cell lymphoma, unclassifiable.

Table 2: Histopathological and Immunophenotypic Comparison

Cytogenetic and molecular findings are summarized in Table 3. Chromosomal abnormalities were identified in one case, including deletion of chromosome 13q14 and trisomy 12. Another case was negative for t (11; 14), helping to exclude mantle cell lymphoma. No cytogenetic abnormality was detected in the third case.

Table 3: Cytogenetic and Molecular Findings

The differential diagnostic considerations and distinguishing features are outlined in Table 4. Major differentials included chronic lymphocytic leukemia/small lymphocytic lymphoma, mantle cell lymphoma, lymphoplasmacytic lymphoma, and marginal zone lymphoma. Final diagnostic interpretation was supported by integration of morphological features, immunophenotypic profile, and clinical findings.

Table 4: Differential Diagnosis Considered

A comprehensive clinicopathological summary of all cases is provided in Table 5, including clinical presentation, primary disease site, immunohistochemical profile, cytogenetic findings, and follow-up outcomes. During follow-up, all patients demonstrated an indolent clinical course with stable disease, with follow-up periods extending up to 48 months.

Table 5: Summary of Clinicopathological Findings

Figure 1:  Case 1-Bone marrow biopsy showing interstitial infiltration by small mature lymphoid cells (Hematoxylin & Eosin stain, ×400)

Figure 2: Case 2- the bone marrow biopsy showing a -paratrabecular infiltrate of small, mature B-cell lymphocytes (Hematoxylin & Eosin stain, ×100)

DISCUSSION

Indolent small B-cell lymphomas represent a heterogeneous group of mature B-cell neoplasms characterized by slow clinical progression but considerable diagnostic overlap in morphology and immunophenotype. Contemporary classification systems, including the World Health Organization (WHO) 5th edition and the International Consensus Classification (ICC), emphasize an integrated diagnostic approach combining morphology, immunophenotyping, cytogenetic findings, and clinical correlation for accurate disease classification [5, 6].

Bone marrow involvement is commonly observed in indolent lymphomas and may occasionally represent the primary site of disease presentation. Previous studies have reported significant marrow infiltration in entities such as marginal zone lymphoma and lymphoplasmacytic lymphoma [7, 8]. In addition, marrow involvement has been described in several indolent lymphoid neoplasms presenting with unexplained cytopenias or monoclonal gammopathy [9, 10]. In the present study, bone marrow involvement was observed in all cases, emphasizing its diagnostic relevance.

Immunophenotyping remains essential in differentiating indolent B-cell lymphomas. Expression of CD20 confirms B-cell lineage, while variable expression of markers such as CD5 may create diagnostic difficulties. Aberrant CD5 positivity has been reported in certain indolent lymphomas and may mimic chronic lymphocytic leukemia or mantle cell lymphoma [11, 12]. In such situations, the absence of Cyclin D1 expression is helpful in excluding mantle cell lymphoma [13].

Monoclonal paraproteinemia is another important finding in indolent lymphomas, particularly lymphoplasmacytic lymphoma, which is commonly associated with IgM monoclonal gammopathy [14]. Therefore, serum protein electrophoresis can serve as a useful adjunct in the diagnostic workup of suspected lymphoid neoplasms. Cytogenetic abnormalities such as deletion of chromosome 13q14 and trisomy 12 have also been reported in indolent lymphoid neoplasms and may overlap with genetic changes seen in chronic lymphocytic leukemia [15].

Clinically, indolent lymphomas generally demonstrate a stable course, and many patients may be managed with observation in the absence of symptomatic disease. This “watch-and-wait” approach has been supported by several clinical studies [16, 17]. However, long-term follow-up remains important because transformation into aggressive lymphoma, such as diffuse large B-cell lymphoma, may occur in a subset of patients [18].

The present study has limitations, including a small sample size and limited molecular testing. Nevertheless, careful clinicopathological correlation provides useful insight into the diagnostic spectrum of indolent small B-cell lymphomas. Overall, these findings highlight the importance of an integrated diagnostic approach combining clinical, morphological, immunophenotypic, and cytogenetic data for accurate classification and appropriate patient management.

CONCLUSION

Indolent small B-cell lymphomas represent a heterogeneous group of lymphoid neoplasms that often display overlapping clinical, morphological, and immunophenotypic features, posing significant diagnostic challenges in routine practice. The present study highlights the importance of a comprehensive diagnostic approach integrating histopathology, immunophenotyping, cytogenetic findings, and clinical correlation for accurate subclassification. Recognition of atypical presentations, including bone marrow–predominant disease and associated monoclonal paraproteinemia, is essential to avoid diagnostic misinterpretation and inappropriate management.

This study contributes to the existing literature by emphasizing real-world diagnostic complexities encountered in indolent lymphoma cases within a tertiary care setting. Improved awareness of these clinicopathological variations may facilitate more precise diagnosis, appropriate risk stratification, and optimized patient management. Continued research with larger cohorts and advanced molecular testing will further enhance understanding of the biological behavior and classification of indolent small B-cell lymphomas.

REFERENCES

1. Sung, H., Ferlay, J., Siegel, R. L., Laversanne, M., Soerjomataram, I., Jemal, A., & Bray, F. (2021). Global cancer statistics 2020: GLOBOCAN estimates of incidence and mortality worldwide for 36 cancers in 185 countries. CA: A Cancer Journal for Clinicians, 71(3), 209–249. https://doi.org/10.3322/caac.21660
2. Swerdlow, S. H., Campo, E., Pileri, S. A., Harris, N. L., Stein, H., Siebert, R., & Jaffe, E. S. (2016). The 2016 revision of the World Health Organization classification of lymphoid neoplasms. Blood, 127(20), 2375–2390. https://doi.org/10.1182/blood-2016-01-643569
3. Nair, R., Arora, N., & Mallath, M. K. (2020). Epidemiology of non-Hodgkin lymphoma in India. The Oncologist, 25(9), e1546–e1554. https://doi.org/10.1634/theoncologist.2019-0760
4. Naresh, K. N., Srinivas, V., & Soman, C. S. (2016). Distribution of various subtypes of non-Hodgkin lymphoma in India: A study using the World Health Organization classification. Indian Journal of Pathology and Microbiology, 59(4), 457–462.
5. Alaggio, R., Amador, C., Anagnostopoulos, I., Attygalle, A., Araujo, I., Berti, E., & Campo, E. (2022). The 5th edition of the World Health Organization classification of haematolymphoid tumours: Lymphoid neoplasms. Leukemia, 36(7), 1720–1748. https://doi.org/10.1038/s41375-022-01620-2
6. Campo, E., Jaffe, E. S., Cook, J. R., Quintanilla-Martinez, L., Swerdlow, S. H., Anderson, K. C., & Chan, W. C. (2022). The International Consensus Classification of mature lymphoid neoplasms. Blood, 140(11), 1229–1253. https://doi.org/10.1182/blood.2022015851
7. Arcaini, L., Rossi, D., & Paulli, M. (2016). Splenic marginal zone lymphoma: From genetics to management. Blood, 127(17), 2072–2081. https://doi.org/10.1182/blood-2015-11-624304
8. Zucca, E., & Bertoni, F. (2016). The spectrum of marginal zone lymphomas. Nature Reviews Clinical Oncology, 13(6), 341–354. https://doi.org/10.1038/nrclinonc.2016.20
9. Matutes, E., Oscier, D., Montalban, C., Berger, F., Callet-Bauchu, E., Dogan, A., & Wotherspoon, A. (2017). Diagnostic criteria for chronic lymphocytic leukemia and related disorders. Leukemia, 31(7), 1472–1479. https://doi.org/10.1038/leu.2017.104
10. Jain, P., Wang, M., & Romaguera, J. (2019). Mantle cell lymphoma: Biology, pathogenesis, and clinical management. Cancer, 125(1), 48–56. https://doi.org/10.1002/cncr.31709
11. Treon, S. P., Xu, L., & Hunter, Z. R. (2015). Waldenström macroglobulinemia. The Lancet, 385(9978), 1560–1572. https://doi.org/10.1016/S0140-6736(14)61179-7
12. Puiggros, A., Blanco, G., & Espinet, B. (2014). Genetic abnormalities in chronic lymphocytic leukemia: Where we are and where we go. Cancer Genetics, 207(9), 349–360. https://doi.org/10.1016/j.cancergen.2014.06.007
13. Ardeshna, K. M., Qian, W., Smith, P., Braganca, N., Lowry, L., Patrick, P., Warden, J., Stevens, L., Pocock, C., Miall, F., et al. (2014). Early treatment versus watchful waiting in patients with advanced stage asymptomatic follicular lymphoma. The Lancet Oncology, 15(4), 424–435. https://doi.org/10.1016/S1470-2045(14)70027-0
14. Shankland, K. R., Armitage, J. O., & Hancock, B. W. (2018). Non-Hodgkin lymphoma. The Lancet, 380(9844), 848–857. https://doi.org/10.1016/S0140-6736(12)60605-9
15. Link, B. K., & Maurer, M. J. (2015). Transformation of indolent lymphoma. Hematology/Oncology Clinics of North America, 29(4), 1035–1048. https://doi.org/10.1016/j.hoc.2015.04.011
16. Sarkozy, C., & Sehn, L. H. (2018). Management of indolent lymphomas. Blood, 131(5), 515–523. https://doi.org/10.1182/blood-2017-09-742593
17. Freedman, A. (2020). Follicular lymphoma: 2020 update on diagnosis and management. American Journal of Hematology, 95(3), 316–327. https://doi.org/10.1002/ajh.25696
18. Morton, L. M., Wang, S. S., Devesa, S. S., Hartge, P., Weisenburger, D. D., & Linet, M. S. (2019). Lymphoma incidence patterns by subtype in the United States. Blood, 134(12), 1023–1034. https://doi.org/10.1182/blood.2019001129