Primary Lung Mucosa-Associated Lymphoid Tissue Lymphoma Accompanied by Multiple Sclerosis: Case Report and Molecular Diagnosis
Lung mucosa-associated lymphoid tissue (MALT) lymphoma represents a rare subset of extranodal marginal zone B-cell lymphomas, predominantly arising in mucosal sites such as the stomach, lung, ocular adnexa, and thyroid. While pulmonary MALT lymphoma accounts for approximately 14% of all MALT lymphomas, its diagnosis remains challenging due to overlapping morphological features with reactive lymphoproliferative disorders. This case report highlights the diagnostic complexities of a rare co-occurrence of pulmonary MALT lymphoma and multiple sclerosis in a 56-year-old male, emphasizing the critical role of molecular clonality testing in confirming malignancy and overcoming histological ambiguities.
Clinical Presentation and Radiological Findings
A 56-year-old man presented to Shanghai Chest Hospital following an incidental discovery of a mediastinal mass during a routine physical examination. The patient reported an unintentional weight loss of 5 kg over an unspecified period but denied respiratory symptoms such as cough or dyspnea. Contrast-enhanced computed tomography (CT) revealed an oval, homogeneously enhancing mass (4.8 cm × 2.7 cm) infiltrating the left anterior mediastinum near the aortic arch. The lesion extended into the left upper lung lobe with irregular borders and was accompanied by multiple bilateral pulmonary nodules. These imaging findings raised suspicion of a neoplastic process, prompting surgical intervention.
Pathological and Immunohistochemical Analysis
Thoracoscopic wedge resection of the left upper lobe yielded a firm, grayish tumor measuring 4.5 cm × 4.0 cm × 2.5 cm beneath the pleura. Histological examination demonstrated dense aggregates of small lymphoid cells arranged in a monocytoid and plasmacytoid growth pattern, interspersed with broad bands of sclerotic tissue. Lymphoepithelial lesions, a hallmark of MALT lymphoma, were focally observed. Tumor cells exhibited pale staining cytoplasm and irregular nuclei without significant atypia.
Immunohistochemistry (IHC) confirmed the B-cell lineage of the neoplastic population, with strong positivity for CD20 and CD79a. Tumor cells were negative for T-cell markers (CD3), cyclin D1, and CD10, ruling out mantle cell lymphoma and follicular lymphoma, respectively. The Ki67 proliferation index was low at 10%, consistent with the indolent nature of MALT lymphomas. However, extensive stromal fibrosis obscured tumor architecture, complicating histological differentiation between malignant and reactive lymphoid infiltrates.
Molecular Clonality Analysis Using BIOMED-2 PCR
To resolve diagnostic uncertainty, BIOMED-2 polymerase chain reaction (PCR) protocols were employed to assess immunoglobulin (IG) gene rearrangements, a gold standard for confirming clonality in B-cell malignancies. Formalin-fixed, paraffin-embedded (FFPE) tissue sections underwent laser capture microdissection to isolate lymphoid cells from fibrotic regions. DNA extraction and purification were performed using a QIAamp DNA mini kit, with 125 ng of DNA input per PCR reaction.
The BIOMED-2 multiplex PCR system targeted immunoglobulin heavy chain (IGH) and kappa light chain (IGK) genes. For IGH, five primer sets (IGHA–IGHE) amplified framework regions 1–3 of the variable (VH) domain and the joining (JH) region. IGK analysis utilized two primer sets (IGKA, IGKB) targeting Vκ-Jκ and Kde-intron recombinations. T-cell receptor (TCR) gene rearrangements were excluded using primer sets for TCRβ, TCRγ, and TCRδ.
Initial PCR attempts using bulk FFPE DNA yielded fragmented control DNA (100 bp) and ambiguous clonality signals due to stromal interference. Repeat testing with microdissected tumor cells improved DNA integrity, yielding a 400-bp control product. Capillary electrophoresis of denatured PCR products detected monoclonal peaks in IGH framework 1 (IGHA) and framework 2 (IGHB) reactions, confirming a clonal B-cell population. Polyclonal background signals were absent, validating the specificity of the assay.
Diagnostic Challenges and Technical Considerations
This case underscores two critical diagnostic hurdles in pulmonary MALT lymphoma: (1) histological overlap with benign lymphoproliferations and (2) technical artifacts introduced by fibrosis in FFPE samples. Broad sclerotic bands disrupted tumor cell architecture, mimicking inflammatory or post-infectious scarring. Furthermore, formalin fixation cross-links DNA, reducing amplifiable fragment sizes and complicating PCR-based clonality testing. The authors emphasize that microdissection enriches tumor cell purity, mitigates stromal interference, and enhances DNA quality for reliable clonality assessment.
Clinical Implications of Coexisting Multiple Sclerosis
The concurrent diagnosis of multiple sclerosis (MS) in this patient raises questions about immune dysregulation as a shared etiological factor. Chronic antigen stimulation—a proposed driver of MALT lymphomagenesis—may theoretically intersect with autoimmune processes in MS. However, no direct molecular link between the two conditions was explored in this study. Future investigations could elucidate whether shared genetic predispositions or microenvironmental factors contribute to this rare association.
Integration of Molecular Diagnostics in Routine Practice
Molecular clonality testing has become indispensable for diagnosing lymphoproliferative disorders, particularly in morphologically ambiguous cases. The BIOMED-2 protocol standardizes PCR conditions across laboratories, enabling reproducible detection of clonal IG/TCR rearrangements. Key considerations for optimal results include:
- Tumor Enrichment: Microdissection or manual macrodissection to isolate neoplastic cells from reactive or fibrotic stroma.
- DNA Integrity: Prioritizing fresh or frozen tissue over FFPE specimens when possible; if using FFPE, ensure DNA fragment sizes >400 bp for reliable amplification.
- Multiplexing: Simultaneous analysis of multiple IG/TCR targets to compensate for primer failure or somatic hypermutation.
- Interpretation Expertise: Close collaboration between pathologists and molecular biologists to correlate clonality data with histomorphology and immunophenotype.
Conclusion
This case exemplifies the diagnostic utility of molecular clonality testing in differentiating pulmonary MALT lymphoma from reactive mimics, particularly in fibrotic contexts. The integration of IHC, histopathology, and BIOMED-2 PCR enabled definitive classification despite confounding sclerosis. Clinicians and pathologists must recognize the impact of pre-analytical variables (e.g., tissue fibrosis, fixation artifacts) on molecular assays and adopt tumor-enrichment strategies to enhance diagnostic accuracy.
doi.org/10.1097/CM9.0000000000000272
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