Primary mediastinal large B-cell lymphoma

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Sowminya Arikapudi, M.B,B.S. [2]

Synonyms and keywords:: Mediastinal B-cell lymphoma; Mediastinal large B-cell lymphoma, PMBCL, Primary mediastinal B-cell lymphoma.

Overview

Primary mediastinal large B-cell lymphoma (PMBCL) is a subtype of diffuse large B-cell lymphoma (DLBCL). It is also considered a distinct type of non-Hodgkin lymphoma (NHL) in the World Health Organization (WHO) classification system. It occurs in the thymus gland. The small gland in the centre of the chest behind the sternum where lymphocytes mature, multiply and become T cells. or lymph nodes in the center of the chest. On microscopic histopathological analysis, large-sized cells and alveolar fibrosis are characteristic findings of primary mediastinal large B-cell lymphoma. The incidence of primary mediastinal large B-cell lymphoma increases with age; the median age at diagnosis is 35 years. Symptoms of the primary mediastinal large B-cell lymphoma include fever, weight loss, night sweats, skin rash, facial swelling, cough, shortness of breath, and painless swelling in the neck, axilla, groin, thorax, or abdomen. Lymph node or mediastinal mass biopsy is diagnostic of primary mediastinal large B-cell lymphoma. The predominant therapy for primary mediastinal large B-cell lymphoma is chemotherapy. Adjunctive radiotherapy, stem cell transplant, and biological therapy may be required. The optimal therapy for primary mediastinal large B-cell lymphoma depends on the clinical presentation.

Pathophysiology

• Primary mediastinal large B-cell lymphoma most likely arises within the thymus.
• Patients present with a localized anterosuperior mediastinal mass.
• The mass is often bulky and frequently invades adjacent structures such as lungs, pleura, or pericardium.
• Spread to supraclavicular and cervical lymph nodes can occur.

Genetics

Genes involved in the pathogenesis of primary mediastinal large B-cell lymphoma include:

• Comparative genomic hybridzation demonstrated gains in chromosome 9p24 and 2p15
• Genomic hybridization in chromosome X-p11.4-21
• Immunoglobulin genes clonally rearranged

Microscopic Pathology

On microscopic histopathological analysis, large-sized cells and alveolar fibrosis are characteristic findings of primary mediastinal large B-cell lymphoma.

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  Hematoxylin and eosin (50X). Primary mediastinal B cells (PMBC) associated with delicate interstitial fibrosis.

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  Primary mediastinal large B-cell lymphoma immunoreactivity for B cell antigen on the membrane, CD20

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  Primary mediastinal large B-cell lymphoma immunoreactivity for CD30

Causes

There are no established causes for primary mediastinal large B-cell lymphoma.

Differentiating type page name here from other Diseases

Primary mediastinal large B-cell lymphoma must be differentiated from other diseases such as:

• Thymoma
• Hodgkin's lymphoma
• Thymic carcinoma

Epidemiology and Demographics

Age

The incidence of primary mediastinal large B-cell lymphoma increases with age; the median age at diagnosis is 35 years.

Gender

Females are more commonly affected with primary mediastinal large B-cell lymphoma than males.

Risk Factors

There are no established risk factors for primary mediastinal large B-cell lymphoma.

Screening

According to the the U.S. Preventive Service Task Force (USPSTF), there is insufficient evidence to recommend routine screening for primary mediastinal large B-cell lymphoma.

Natural History, Complications and Prognosis

• Primary mediastinal large B-cell lymphoma is usually a fast-growing (aggressive) lymphoma.
• Patients often have localized disease in the chest at first.
• If left untreated, primary mediastinal large B-cell lymphoma can cause shortness of breath, cough, or chest pain as the mass grows in the chest.
• Primary mediastinal large B-cell lymphoma can also partially block the main vein (superior vena cava) that carries blood from the upper body to the heart and cause superior vena cava syndrome.
• The bone marrow is rarely affected by this type of lymphoma.
• Recurrence or relapse often occurs in organs or tissues outside the lymph nodes (extranodal sites), such as the kidneys or central nervous system.

Diagnosis

Staging

Staging for primary mediastinal large B-cell lymphoma is provided in the following table:

Revised staging system for primary nodal lymphomas (Lugano classification)

Stage	Involvement	Extranodal (E) status
Limited
Stage I	One node or a group of adjacent nodes	Single extranodal lesions without nodal involvement
Stage II	Two or more nodal groups on the same side of the diaphragm	Stage I or II by nodal extent with limited contiguous extranodal involvement
Stage II bulky	II as above with "bulky" disease	Not applicable
Advanced
Stage III	Nodes on both sides of the diaphragm; nodes above the diaphragm with spleen involvement	Not applicable
Stage IV	Additional noncontiguous extralymphatic involvement	Not applicable

Symptoms

Symptoms of the primary mediastinal large B-cell lymphoma include:

• Fever
• Weight loss
• Night sweats
• Skin rash
• Shortness of breath
• Facial swelling
• Cough
• Painless swelling in the neck, axilla, groin, thorax, and abdomen

Physical Examination

Vitals

• Fever is often present

Skin

• Rash

HEENT

• Cervical lymphadenopathy
• Facial edema

Thorax

• Thoracic masses suggestive of central lymphadenopathy
• Localized anterosuperior mediastinal mass

Abdomen

• Abdominal masses suggestive of central lymphadenopathy

Extremities

• Peripheral lymphadenopathy

Laboratory Findings

Laboratory tests for primary mediastinal large B-cell lymphoma include:

• Complete blood count (CBC)
• Blood chemistry studies
• Cytogenetic analysis
• Flow cytometry
• Immunohistochemistry
• Immunophenotyping:

• Positive: CD19, CD79a, CD20, CD30, and CD22

Chest X-Ray

Chest X-ray may be helpful in the diagnosis of primary mediastinal large B-cell lymphoma. Finding on chest X-ray suggestive of primary mediastinal large B-cell lymphoma includes large anterior mediastinal mass.

Biopsy

Lymph node or mediastinal mass biopsy is diagnostic of primary mediastinal large B-cell lymphoma.

Echocardiography

Echocardiography may be helpful in the diagnosis of primary mediastinal large B-cell lymphoma.

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  A comprehensive 2 dimensional M-mode color flow and Doppler echocardiography reveals a normal left ventricular systolic function (EF 60–69%). A large right atrial mass measuring  cm almost fills the right atrium and extends into the tricuspid valve causing tricuspid regurgitation.

CT

CT scan may be helpful in the diagnosis of primary mediastinal large B-cell lymphoma.

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  CT scan of the chest with contrast reveals a large lobulated anterior mediastinal solid mass (black arrow) with extension into the right hemithorax and the right atrium. There is displacement of the great vessels into the left hemithorax with significant mass effect on the right upper lobe. The tumor causes compression of the right pulmonary artery (red arrow) and right and left mainstem bronchi (white arrows).

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  Coronal CT scan image elucidates a mediastinal mass with extension into the right atrium (black arrow) with complete encasement and compression of the SVC. The tumor extends to the confluence of the IVC in the right atrium causing dilatation of the intraabdominal IVC and hepatic veins suggesting compromised cardiac return (red arrows). Tumor causes the displacement of great vessels into the left hemithorax.

MRI

MRI scan may be helpful in the diagnosis of primary mediastinal large B-cell lymphoma.

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  Cardiac MRI short axis T1 at the level of mitral valve reveals a large mediastinal mass infiltrating and obliterating the SVC causing SVC obstruction. The tumor extends into the right atrium (red arrow) and invades the tricuspid valve.

Other Imaging Findings

PET scan may be helpful in the diagnosis of primary mediastinal large B-cell lymphoma.

Treatment

Medical Therapy

Treatment of primary mediastinal large B-cell lymphoma

Therapy	Description
Chemotherapy	A commonly used combination chemotherapy is CHOP: Cyclophosphamide, Doxorubicin, Vincristine, AND Prednisone
Biological therapy	Rituximab may be added to chemotherapy.
Radiation therapy	External beam radiation therapy to the mass in the chest may be used after chemotherapy.
Stem cell transplant	A stem cell transplant may be offered to some people if their lymphoma returns or relapses after treatment.