ALK-positive large B-cell lymphoma

Epidemiology and Etiology:

• < 40 cases reported (rare)
• M:F 3:1
• All age groups (median 36 y)

Common sites:

• Lymph nodes mainly
• Mediastinum
• Extranodal sites

Gross features:

Histologic features:

• Sinusoidal growth pattern
• Immunoblast-like B cells
• Monomorphic
• Large
• Round pale nuclei
• Large central nucleoli
• Abundant cytoplasm
• Plasmablastic differentiation sometimes
• Atypical multinucleated neoplastic giant cells maybe

Immunophenotype:

Marker:	Sensitivity:	Specificity:
ALK (strong, granular, cytoplasmic) (maybe nuclear nucleolar cytoplasmic)
EMA
CD138
VS38
CD3 (neg)
CD20 (neg)
CD79a (neg)
CD45 (weak or neg)
CD30 (neg)
Ig (cytoplasmic, usually IgA)
Light chain restriction
CK (some)
CD4 (some)
CD57 (some)
IRF4/MUM1 (some)
CD43 (focally)
Perforin (maybe)

Molecular features:

• Lacking t(2;5)
• Clonally rearranged immunoglobulin genes
• ALK fusion protein (chr 2)
• t(2;17)(p23;q23) (CLTC-ALK) fusion
• t(2;5)(p23;35) (few) (as in ALK-positive T/Null anaplastic large cell lymphoma (ALCL)
• may be due to cryptic insertion into 4q22-24

Other features:

• median survival 11 months for high-stage

References:

• WHO blue book (2008)