Primary pulmonary MALT lymphoma

A 69-year-old man presented with dry cough and dyspnea. He had a history of chronic obstructive pulmonary disease and rectal cancer, successfully treated with surgical resection and chemoradiotherapy. He was an ex-smoker. Physical examination revealed weak vesicular breath sounds and normal vital signs. Laboratory findings were unremarkable.

X-ray (Figure 1) shows bilateral airspace consolidations.

CT (Figure 2) shows multiple well-delineated soft-tissue masses with air bronchogram and halo sign, the largest one measuring 9 cm in the inferior left lobe. There are also multiple lung cysts, with mid to lower-lobe predominance. No evidence of hilar or mediastinal lymphadenopathy.

PET-CT (Figure 3) shows pulmonary consolidation areas with 18FDG uptake in both lungs (SUVmax 9.9).

CT-guided transbronchial biopsy was performed. The histopathology of the tissues revealed a small to intermediate-sized B lymphocyte cell population with towel-like growth and hyalinized areas. On immunohistochemistry, the tumour showed positivity for CD20, CD79, Bcl2 and CD43 and negativity for Bcl6, CD3, CD5, CD10 and cyclin D1. There was focally positivity for MUM1. The proliferation index (Ki67) was 20%. This was compatible with a pulmonary mucosa-associated lymphoid tissue (pMALT) lymphoma.

He also underwent a bone marrow aspirate and upper endoscopy, which were normal.

Background

Pulmonary MALT lymphoma is the most frequent primary pulmonary lymphoma, which is a rare clinical entity [1]. It is a low-grade B-cell extranodal lymphoma characterized by a proliferation of clonal marginal zone lymphocytes and is associated with chronic antigenic stimulation and autoimmune diseases, such as systemic lupus erythematosus, Hashimoto’s thyroiditis, and Sjögren’s syndrome [2].

Clinical Perspective

Pulmonary MALT lymphoma usually occurs in sixth and seventh decade. Patients might be asymptomatic or present with unspecific symptoms and signs with a slow and insidious course. Most common symptoms are cough, dyspnea, expectoration, chest pain, hemoptysis, and B symptoms [3].

Imaging Perspective

On imaging, it typically manifests as solitary or multiple consolidations with air bronchograms, nodules, masses, and ground glass opacifications or as a pattern of diffuse interstitial lung disease. Hilar or mediastinal lymphadenopathy might also be present [4,5].

PET-CT is useful for staging, and most lesions demonstrate increased FDG avidity.

Pulmonary MALT lymphoma can only be reliably diagnosed by pathology. Transbronchial or CT-guided transthoracic lung biopsy and surgical resection can be used to obtain samples for pathologic diagnosis [6].

Outcome

Patients usually have a favourable outcome, with a 5-year overall survival of >85% and a median survival time of over 10 years [7]. Nevertheless, systemic dissemination and transformation into high-grade B-cell lymphoma may occur.

Therapeutic strategies and guidelines remain under debate, mainly due to the limited availability and heterogeneity of the data reported in the literature. Wait-and-watch approach might be considered in asymptomatic patients. Treatment options include surgery, radiotherapy, chemotherapy, immunotherapy, and or a combination of these options [6].

Take Home Message / Teaching Points

Primary pulmonary MALT lymphoma is a rare low-grade B-cell non-Hodgkin’s lymphoma with an indolent course.

The radiographic findings are nonspecific and include a solitary nodule, multiple ill-defined nodules, or consolidated masses with air bronchogram signs. It can easily be misdiagnosed as other lung pathologies like infection or lung cancer.

Biopsy is required for diagnosis.