Introduction
Lymphoma is a malignant (cancerous) condition arising from the lymphocytes (cells that are produced in the bone marrow and are present in the blood and lymph tissues) or lymphoblasts (a lymphocyte that becomes larger after stimulation by an antigen). Lymphomas affect the lymphatic system, including the lymph nodes, thymus gland, spleen, and bone marrow. Lymphomas can also affect other organs in the body. Lung lymphoma refers to the lung involvement in lymphoma, and it can be primary or secondary. Primary pulmonary (lung) lymphoma refers to lymphoid proliferations (abnormal growth of lymphocytes) that affect the lungs without any evidence of extrapulmonary involvement.
What Is Primary Lung Lymphoma?
Primary lung lymphoma is a rare condition and is usually seen in non-Hodgkin's lymphoma (cancer that develops in the lymphatic tissues and lymph nodes in the body). It is a disease of clonal lymphoid proliferation that affects one or both lungs. It is rare compared to secondary lung lymphoma and is thought to represent 0.5 percent of all primary lung cancers and three to four percent of extranodal non-Hodgkin’s lymphoma.
Primary lung lymphomas are a rare subtype of extranodal lymphomas, and lung involvement is usually seen secondary to cancers and recurrent diseases. The lung involvement in primary pulmonary lymphoma includes extranodal marginal lymphoma of multifocal mucosa-associated lymphoid tissue origin (MALT), lymphomatoid granulomatosis, and diffuse large B-cell (bone marrow-derived cells). Primary lymphomas of the lung involve lymphoid proliferations that affect the lungs without any extrapulmonary involvement.
How Do Primary Lung Lymphomas Develop?
Lymphoma refers to a cancer of the lymphatic system, which includes the lymph nodes, thymus gland, bone marrow, and spleen, and may affect other organs in the body. It also includes Hodgkin’s lymphoma and non-Hodgkin’s lymphoma. In rare cases, lymphomas develop in the lungs. Lung lymphoma refers to the parenchymal (functional tissue of the lungs) involvement of the lungs.
Primary lung lymphoma is usually non-Hodgkin's lymphoma which is limited to one or both lungs with or without mediastinal node involvement and without any evidence of extrathoracic dissemination (spread outside the thoracic cavity) for at least three months from the time of initial diagnosis. In less than one percent of cases, primary lung lymphoma represents Hodgkin's lymphoma without any extrapulmonary spread.
Lymphoma develops when a cell in the lymph node or other lymphatic structure undergoes changes (mutations). Mutations can occur in B-lymphocytes (bursa-derived cells which produce antibodies to eliminate infections), T-cells (thymus-derived cells that help B-cells to produce antibodies), or natural killer cells which attack the tumor cells or infected cells. Mutations result in the formation of abnormal lymphocytes. These abnormal lymphocytes exhibit uncontrolled growth and result in the production of excessive abnormal cells. These lymphoma cells or abnormal lymphocytes accumulate to form masses called tumors. If left untreated, these cancerous cells overgrow the white blood cells and disrupt their function against infections. Lymphoma can develop or spread to other body regions where lymphoid tissues are present.
These abnormal lymphoid proliferations can affect the lungs in three ways:
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By hematogenous dissemination (spread through the bloodstream) of Hodgkin’s disease or Non-Hodgkin’s lymphoma.
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By constant invasion from the mediastinal or hilar nodal lymphoma.
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By primary lung involvement.
Lymphoma can develop or spread to the lungs and result in compromised lung function.
What Are the Signs and Symptoms of Primary Pulmonary Lymphoma?
Primary pulmonary lymphoma usually does not cause any symptoms, and the patient remains asymptomatic. In some cases, a lymphoma that develops in the lungs can cause breathing difficulties, pleural effusion (fluid accumulation in the lungs), and a swollen face. Lung lymphoma may compress the nearby structures like the trachea (windpipe) and cause breathing difficulties, coughing, chest pain, tightness in the chest, and hemoptysis (coughing up blood) may be present in some cases. Other symptoms like fever and unintended weight loss may be present. In less than 20 percent of cases, crackles (abnormal lung sounds) are observed on auscultation.
How Is Primary Pulmonary Lymphoma Diagnosed?
The diagnosis depends on the symptoms and the radiological findings. As these symptoms are non-specific, the diagnosis depends on the radiological features. About 50 to 90 percent of cases present radiological features, like localized alveolar opacity with blurred or well-defined contours.
CT (computed tomography) scan helps determine the presence of bilateral and multiple lesions with distended bronchi (two tubes that carry air from the windpipe to the lungs), which is a significant diagnostic sign. It can also reveal pleural effusion, atelectasis (collapsed lung), and mediastinal adenopathies (enlargement of mediastinal nodes in response to infection or cancer).
Based on the radiologic abnormalities, lung lymphomas are categorized into consolidation, masses, nodules, ground-glass opacity, and lymphangitis or perilymphatic patterns. Consolidation refers to a homogenous increase in lung parenchymal attenuation (mosaic pattern) which obscures the airway walls and vessel margins. Mass refers to well-defined or moderately well-defined opacity, which is fewer than three centimeters in diameter. Nodule is a well-defined or moderately well-defined opacity over three centimeters in diameter. Ground glass opacity refers to a hazy lung attenuation with the preservation of airway walls and vascular margins. The diagnosis depends on these radiographic features and the presence of features such as mosaic patterns, pleural effusions, mediastinal lymphadenopathy, calcification, and cavitation.
MALT-type primary lung lymphoma is diagnosed based on the histological examination of surgical samples or tissues obtained from a transbronchial, transthoracic, or bronchial biopsy.
How Is Primary Lung Lymphoma Treated?
The treatment options available for primary lung lymphoma are surgical resection, chemotherapy, and radiotherapy. However, the efficacy of these treatments cannot be determined due to a lack of comparative studies. In some cases, clinical monitoring is preferred.
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Surgical Resection: It is usually performed for localized lung lymphomas.
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Chemotherapy: It is used for cases with bilateral or extrapulmonary involvement and relapsing or progressing lymphomas. Chemotherapeutic drugs, such as Cyclophosphamide, Azathioprine, Chloraminophene, and steroids, are more effective.
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Radiotherapy: It is rarely used in the treatment of primary lung lymphoma.
Conclusion
Lymphomas are malignant cancers that arise from the cells of the lymphatic system. Primary lung lymphoma denotes lymphomas that originate or spread to the lungs. Primary lung lymphoma is a rare cancerous condition with non-specific symptoms. Various advancements in diagnostic procedures help in the diagnosis of this condition, though it is difficult to differentiate from lung cancer. In addition, the prognosis of this condition depends on the stage and the nature of the lymphoma. Individuals with slow-growing lymphomas have good outcomes.
