Primary Systemic Anaplastic Large Cell Lymphoma
Definition
- Systemic CD30+ T cell lymphoma usually composed of cohesive large cells witih abundant cytoplasm and pleomorphic nuclei; half or more express anaplastic lymphoma kinase (ALK1)
Alternate/Historical Names
- Anaplastic large cell lymphoma (T/null cell type)
- Ki-1 lymphoma (included some cases of diffuse large B cell lymphoma)
Diagnostic Criteria
- Cohesive large cells with abundant cytoplasm and pleomorphic nuclei
- Hallmark cells (“horseshoe cells”)
- Characteristic large cells with U-shaped or C-shaped nuclei surrounding a brightly eosinophilic Golgi area
- Most frequent in the common variant
- Scattered hallmark cells usually also found in small cell, lymphohistiocytic and other variants
- Cohesive growth pattern
- Intrasinusoidal growth in lymph nodes (if lymph node is not effaced)
- Numerous histological variants have been described, and may coexist
- Common variant
- large anaplastic cells with abundant eosinophilic cytoplasm and pleomorphic nuclei
- Small cell variant
- Smaller cells with less irregular nuclei than common variant
- Hallmark cells in perivascular location
- Lymphohistiocytic variant
- Predominance of histiocytes
- Hallmark cells in perivascular location
- Less common subtypes: neutrophil-rich, giant cell rich, signet ring, sarcomatoid, Hodgkin-like with nodular sclerosis
- Common variant
- Hallmark cells (“horseshoe cells”)
- T cell or “null cell” immunophenotype
- Lack of B cell or classical Hodgkin immunophenotype
- ALK1 immunopositivity/ALK1 translocation is definitional in this setting, but is absent in up to 40% of cases
- It is debated by some experts that ALK1-negative cases should be classified as peripheral T-cell lymphoma, NOS
- A rare set of large B cell lymphomas express ALK1
- May involve multiple lymph node and soft tissue sites, including skin, but must not be limited to the skin
- See primary cutaneous anaplastic large cell lymphoma
Dita Gratzinger MD PhD
Yasodha Natkunam MD PhD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342
Initial posting : September 29, 2007