ALK Expression Defines a Distinct Group of T/Null Lymphomas (“ALK Lymphomas”) with a Wide Morphological Spectrum

Abstract

The t(2;5)(p23;q35) translocation associated with CD30-positive anaplastic large cell lymphoma results in the production of a NPM-ALK chimeric protein, consisting of the N-terminal portion of the NPM protein joined to the entire cytoplasmic domain of the neural receptor tyrosine kinase ALK. The ALK gene products were identified in paraffm sections by using a new anti-ALK (cytoplasmic portion) monoclonal antibody (ALKc) that tends to react more strongly than a previously described ALK1 antibody with the nuclei of ALK-expressing tumor cells after microwave heating in 1 mmol/L ethylenediaminetetraacetic acid buffer, pH 8.0. The ALKc monoclonal antibody reacted selectively with 60% of anaplastic large cell lymphoma cases (60 of 100), which occurred mainly in the first three decades of life and consistently displayed a T/null phenotype. This group of ALK-positive tumors showed a wide morphological spectrum including cases with features of anaplastic large cell lymphoma "common" type (75%), "lymphohistiocytic" (10%), "small cell" (8.3%), "giant cell" (3.3%), and "Hodgkin's like" (3.3%). CD30-positive large anaplastic cells expressing the ALK protein both in the cytoplasm and nucleus represented the dominant tumor population in the common, Hodgkin's-like and giant cell types, but they were present at a smaller percentage (often with a perivascular distribution) also in cases with lymphohistiocytic and small cell features. In this study, the ALKc antibody also allowed us to identify small neoplastic cells (usually CD30 negative) with nucleus-restricted ALK positivity that were, by definition, more evident in the small cell variant but were also found in cases with lymphohistiocytic, common, and "Hodgkin's-like" features. These findings, which have not been previously emphasized, strongly suggest that the neoplastic lesion (the NPM-ALK gene) must be present both in the large anaplastic and small tumor cells, and that ALK-positive lymphomas lie on a spectrum, their position being defined by the ratio of small to large neoplastic cells. Notably, about 15% of all ALK-positive lymphomas (usually of the common or giant cell variant) showed a cytoplasm-restricted ALK positivity, which suggests that the ALK gene may have fused with a partner(s) other than NPM. From a diagnostic point of view, detection of the ALK protein was useful in distinguishing anaplastic large cell lymphoma cases of lymphohistiocytic and small cell variants from reactive conditions and other peripheral T-cell lymphoma subtypes, as well as for detecting a small number of tumor cells in lymphohemopoietic tissues. In conclusion, ALK positivity appears to define a clinicopathological entity with a T/null phenotype ("ALK lymphomas"), but one that shows a wider spectrum of morphological patterns than has been appreciated in the past.

TPM3-ALK and TPM4-ALK Oncogenes in Inflammatory Myofibroblastic Tumors

“…Previous studies, in anaplastic large-cell lymphoma, have shown that cellular sublocalization patterns, for the various ALK fusion oncoproteins, are consistent and distinctive. [25][26][27] In some cases, eg, NPM-ALK, a characteristic localization results from shuttling of fusion oncoprotein heterodimers to those cellular structures with which the ALK fusion partner is normally associated. 28 The subcellular localization patterns establish morphological signatures for the different ALK fusion proteins, notwithstanding the fact that the major site of oncogenic action-at least with respect to activation of ALK signaling pathways-is undoubtedly cytoplasmic.…”

Activation of Rac1 and the exchange factor Vav3 are involved in NPM-ALK signaling in anaplastic large cell lymphomas

“…Activation of the Rho GTPases was first studied in two NPM-ALK positive ALCL cell lines, Karpas 299 (common type) and Cost (small cells, aggressive variant) (Falini et al, 1998;Lamant et al, 2004). Pull-down assays demonstrated that Rac1 was strongly activated in both cell lines (Figure 1a).…”

Expression of the oncogenic NPM-ALK chimeric protein in human lymphoid T-cells inhibits drug-induced, but not Fas-induced apoptosis

“…The ALK1 and ALKc (Falini et al, 1998) mAbs, which recognize the intracellular, kinasecontaining region of ALK, have been described previously. The anti-Fas (CD95, clone CH11) and anti-phosphotyrosine (clone 4G10) mAbs were purchased from Upstate Biotechnology (Lake Placid, NY, USA), anti-actin mAb (clone AC-10) from Sigma, anti-cytochrome c mAb from Pharmingen (San Diego, CA, USA), anti-cytochrome oxidase subunit II mAb from Molecular Probes (Eugene, OR, USA), polyclonal rabbit anti-human phosphorylated Akt (serine 473) antibody from New England Biolabs (Beverly, MA, USA), and peroxidase-conjugated rabbit anti-mouse and pig anti-rabbit Ig antisera from Dako (Glostrup, Denmark).…”

“…Cells were cytospun onto glass slides coated with silane, ®xed in acetone for 10 min, and stained using ALK1 or ALKc (Falini et al, 1998) mAb in a three stage immunoperoxidase technique (Benharroch et al, 1998).…”