Primary Pulmonary Lymphoma

(aka Mucosa-Associated Lymphoid Tissue, MALT-Associated Lymphoma)

Epidemiology: accounts for <5% of all extranodal NHL

  • Increased incidence in AIDS (although AIDS-related NHL are intrathoracic in <10% of cases)

Pathogenesis

  • NHL arising from mucosa-associated lymphoid tissue in the lung
  • Usually multicentric or diffuse (due to lack of focal lymphoid tissue in lung): may present as isolated masses, peribronchial proliferation, or interstitial infiltration
  • Pattern of Spread: diffuse spread with poorly-defined margins (spread to intrathoracic nodes/ vessel invasion, tumor necrosis are uncommon)

Pathology

  • Usually low-grade lymphomas (except AIDS cases, which are usually high-grade B-cell types)
  • Usually small B-cells with cleaved nuclei/ reactive-appearing germinal centers

Diagnosis

  • FOB: BAL lymphocytosis (>35%) may be seen (also seen in Sarcoid, Berylliosis, HP, drug-induced ILD, LIP)
    -Normal BAL lymphocyte percentage: <15%
    -TBB may be diagnostic

OLB: usually required (but diagnosis is often difficult)
-Identification of the cells as monoclonal is necessary to rule out benign reactive lymphoid proliferation
-Immunohistochemical stains: may aid in identify B-cell origin

CXR/Chest CT Patterns:
1) “Bronchovascular-Lymphangitic” Pattern: presents as diffuse reticulonodular infiltrates
2) “Alveolar” Pattern: may be segmental or lobar, resembles pneumonia
3) “Nodular” Pattern (small and large nodules): most common pattern
-Lower-lobe predominance
-Nodules may cross fissures
-Nodules may have air bronchograms
-Nodules may cavitate
4) Pleural Effusion:

PET Scan: positive
-Useful to follow after therapy (as scan should revert to PET-negative): recurrence may be manifested by return to being PET-positive


Clinical

  • Symptoms (many patients are asymptomatic):
    -Cough/dyspnea/chest pain:
    -Extranodal disease (25% of cases): BM/orbit/salivary gland
    -Fever/ weight loss are uncommon

Signs:
-Lymphadenopathy usually absent

Complications:
-Transformation to high-grade NHL (in <50% of cases): usually portends poor prognosis


Treatment

  • Asymptomatic: may not require treatment

Symptomatic: surgical resection is preferred for resectable disease
-XRT: for unresectable or incompletely resected disease
-Chemo: for extensive disease only
-Steroids: have been used


Prognosis

  • 50% of deaths occur due to the lymphoma itself and 50% occur due to other causes
  • 5-year survival overall: 88%