Abstract
Diffuse large Bโcell lymphoma positive for anaplastic lymphoma kinase (ALK^+^ DLBCL) is a rare variant of diffuse large Bโcell lymphoma, with characteristic morphological, immunohistochemical and cytogenetic features. Only 34 cases of ALKโpositive diffuse large Bโcell lymphoma have so far been reported in the literature. We examined three new cases, which showed similar characteristics to previously reported cases, but with peculiar nuclearโmembrane staining for ALK protein in one patient and a 5โฒโALK gene deletion in another. All of them had stage IV disease at initial presentation, with poor outcomes. The tumour cells showed immunoblastic/plasmablastic histology and were positive for ALK and Oct2, but negative for CD3, CD20, CD79a, CD30 and PAX5. The staining pattern of ALK protein was cytoplasmic in two patients and associated with the nuclear membrane in one patient. Fluorescence in situ hybridization (FISH) analysis using the ALK breakโapart probe revealed ALK gene rearrangements in all three patients, with a 5โฒโALK gene deletion in one patient. These three cases suggest that different types of cytogenetic aberrations may involve the ALK gene in ALKโpositive diffuse large Bโcell lymphoma leading to peculiar immunohistochemical staining patterns. Copyright ยฉ 2008 John Wiley & Sons, Ltd.