Anaplastic large cell lymphoma (ALK+/ALK-)
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Anaplastic large cell lymphomas (ALCL) are group of mature T-cell lymphoma first described in 1985 as a large-cell neoplasm with anaplastic morphology immunostained by the Ki-1 antibody, which recognizes CD30.
The WHO classification of haematolymphoid tumors recognizes three distinct entities:
ALK-positive anaplastic large-cell lymphoma
ALK-negative anaplastic large-cell lymphoma
As the latter is substantially different in epidemiology, imaging, and prognosis, it is described separately.
ALK+ ALCL is most commonly encountered in children, adolescents and young adults (median age 30 years). It is rare, accounting for only 3% of adult non-hodgkin lymphomas 4.
In contrast, ALK- ALCL are typically encountered in older adults (median age 54 years).
Both are more common in males 4,5.
Presentation is typically either with a mass or with B symptoms (most common in advanced disease).
In the majority of ALK+ ALCL cases, lymph nodes are involved (90%), with extranodal involvement fairly commonly encountered, most commonly of skin, soft tissues, bone, and lung 4.
In contrast, ALK- ALCL cases are more commonly extranodal with approximately half of patients presenting with a single site of disease 5. Soft tissues, breast, liver, bone, mediastinum, and gastrointestinal tract are encountered 5.
Both ALK+ and ALK- ALCL are rare in the central nervous system, most commonly presenting as one or more masses of the supratentorial parenchyma. Involvement of the posterior fossa is less common. Spinal cord, meningeal or skull involvement is rare 3.
These tumors are characterized by large anaplastic cells typically with an eosinophilic paranuclear area adjacent to "bean-shaped" nuclei 3.
Both ALK+ and ALK- tumors are CD30 positive.
ALK+ tumors demonstrate anaplastic lymphoma kinase (ALK) gene rearrangements, and are positive for EMA 3.
Treatment and prognosis
Treatment is primarily with chemotherapy; allogenic transplant is reserved for cases that do not respond 4.
ALK+ ALCL has a fairly good prognosis, substantially better than ALK- tumor, with 80% long-term survival 4. Poor prognostic features include:
central nervous system involvement