Cell fractionation studies of the t(2;5) translocation-containing lymphoma cell line SUP-M2 showed NPM-ALK to be localized within both the cytoplasmic and nuclear compartments.
However, nucleolar accumulation of nucleophosmin-ALK may not be necessary for its oncogenic action, because an ALK protein expressed in a lymphoma carrying a variant (1;2) chromosomal translocation did not accumulate in nucleoli.
Although initially found in primary nodal ALCL, recent studies suggest that NPM-ALK expression may occur in lymphoma at extranodal sites, including the skin; it remains controversial, however, whether CD30+ primary cutaneous lymphoma and its benign counterpart, lymphomatoid papulosis (LyP), express NPM-ALK in some cases.
Immunocytochemical labeling with these antibodies can therefore confirm that an ALK-positive lymphoma expresses NPM-ALK (rather than a variant ALK-fusion protein) and may also provide evidence for chromosomal anomalies involving the NPM gene other than the classical (2;5) translocation.
Whilst the strong labelling for phosphotyrosine observed in the lymphoma cells is due to the presence of activated ALK, the strong staining of some normal cells presumably represents physiologically active kinases and this should be taken into account when interpreting the immunostaining of non-lymphoid tumours.
These results suggest that lymphomas carrying variants of the NPM-ALK fusion protein can be detected by immunostaining for ALK and NPM and also that they can be grouped with classical t(2;5)-positive tumors as a single entity (ALK-positive lymphoma or "ALKoma") that shows a better prognosis than ALK-negative anaplastic large-cell lymphoma.
These 2 cases, therefore, represent a hitherto undescribed mechanism of ALK activation in lymphoma and further illustrate the diversity of fusion partners for the ALK gene.
The term ALKlymphoma signifies a switch in the use of the diagnostic criteria: cases are selected on the basis of a genetic abnormality (the ALK rearrangement), instead of the review of morphological or immunophenotypical features which are clearly more prone to disagreement and controversy.
The initial identification of the ALK gene, expressed as C-terminal part of the transforming fusion protein NPM-ALK in the t(2;5)(p23;q35)lymphoma-associated chromosomal translocation, revealed a novel receptor tyrosine kinase (RTK).
These findings provide further evidence of the breakpoint heterogeneity in ALK translocations and highlight the importance of ALK immunostaining in the diagnosis of ALCL and the identification of the underlying genetic abnormalities in this lymphoma.
We studied 24 anaplastic large cell lymphomas (ALCL) classified by World Health Organization criteria [17 primary nodal/systemic (10 ALK+, 7 ALK-), seven primary cutaneous], and 17 additional non-Hodgkin's lymphomas [one ALK+ B-lineage lymphoma, 14 ALK- diffuse large B-cell lymphomas (seven anaplastic variants, five nonanaplastic, two secondary CD30+), two follicular lymphomas].
This report describes a primary gastric ALK-positive B-lineage lymphoma in which a clathrin (CLTC)-ALK fusion was identified by RT-PCR and direct sequencing of the breakpoint.
No such "signalosome" is found in rafts of ALK(+) T lymphoma and Hodgkin-derived cell lines, despite similar Cbp/PAG, Lyn, and STAT3 expression and similar amounts of raft sphingolipids.
Finally, they suggest that future immunotherapeutic protocols for this type of lymphoma may need to include the inhibition of NPM/ALK and STAT3 to achieve optimal clinical efficacy.
Except in ALK-positive anaplastic large cell lymphoma, defined by ALK gene fusions, chromosomal translocations are otherwise rare in PTCLs, but some recurrent rearrangements might be associated with distinct lymphoma subtypes.
Diffuse large B-cell lymphoma (DLBCL) with plasmablastic features associated with t(2;17)(p23;q23) and characteristic granular cytoplasmic anaplastic lymphoma kinase-1 (ALK1) protein expression is a rare lymphoma subtype.
Gene expression profiling was performed on 144 cases of PTCL and natural killer cell lymphoma and robust molecular classifiers were constructed for angioimmunoblastic T-cell lymphoma (AITL), anaplastic lymphoma kinase-positive (ALK(+)) anaplastic large-cell lymphoma (ALCL), and adult T-cell leukemia/lymphoma.
Thus, our results show (1) that NPM-ALK and TPM3-ALK oncogenes are sufficient for lymphoma/leukemia development and required for tumor maintenance, hence validating ALK as potentially effective therapeutic target; and (2) for the first time, in vivo, the equal tumorigenic potential of the NPM-ALK and TPM3-ALK oncogenic tyrosine kinases.
The anaplastic lymphoma kinase (ALK) gene is frequently involved in translocations that lead to gene fusions in a variety of human malignancies, including lymphoma and lung cancer.