ALK+ large B-cell lymphoma

Upregulation of ALK is mainly due to chromosomal translocation t(2;17), resulting in a fusion gene of CLTC with ALK,^[4][7] but can rarely be due to t(2;5), fusing NPM1 with ALK;^[2]: 378 the later is the usual finding in anaplastic large cell lymphoma (ALCL).^[4][7] The t(2;17) translocation occurs in less than 1% of cases of ALK+ ALCL, but has been identified in inflammatory myofibroblastic tumors.^[3]

There is no association with Epstein–Barr virus^{[2]: 378 [6]} or HHV8,^[6] or immunosuppression.^[2]: 378 The cells are CD20 and CD30 negative,^[8]: 306 showing weak focal expression in 3% and 6% respectively.^[2]: 378 They are EMA and CD138 positive,^[8]: 306 showing 100% expression respectively.^[2]: 378

The median age of diagnosis is approximately late thirties to early forties.^{[2]: 378 [3][5]} The estimates of childhood disease vary (8%,^[9] 15%,^[3] 30%^[2]: 378) but it can be seen at any age.^{[5][8]: 306}

The disease usually arises in lymph nodes, particularly the neck, but extranodal involvement, including in the gastrointestinal tract, nasal cavity, ovary and brain, has been described.^[3][5] Morphologically, there are large immunoblast-like cells with large central nucleoli, often cellular clusters, with a predilection for the lymph node sinuses^{[2]: 378 [4][8]: 306} in a cohesive pattern that can suggest carcinoma cells.^{[2]: 378 [8]: 306}