ANKLAggressive Natural Killer-Cell Leukemia
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ANKL is an extremely rare and aggressive lymphoid neoplasm characterized by a proliferation of EBV-transformed mature NK cells, with a higher incidence in Asia and Central and South America [9].
Similarly to that typically found in other ANKL cases, our patient was very ill, with fever, cytopenias, liver function disturbances, and high levels of serum LDH; and, as in other ANKL cases, the disease affected mainly the BM and the PB, as well as the liver and the spleen.
The immunophenotype of ANKL cells is indistinguishable from that observed in ENKTL for the majority of the currently used markers, and previously published data would suggest that both diseases originate from [CD56.sup.+high] and [CD16.sup.-/+low] NK cells in most cases [17].
To the best of our knowledge, so far, no individual cases of CD56 negative ANKL have been previously described in the literature, although a rare case of aggressive T cell large granular lymphocyte leukemia was recently reported [29], and a case series have revealed strong CD56 positivity in all but 5 cases of 43 (88.4%) of ANKL tested by flow cytometry (11).
Overall, the EBV infection was documented in more than 85% of ANKL cases.
Currently, genetic abnormalities specific for ENKTL and ANKL have not yet been identified, although complex chromosomal aberrancies occur in a large fraction of cases [33].
An array-based comparative genomic hybridization study indicates that the genetic aberrancies recurrently observed in ANKL, which include loss of 7p15.1-p22.3 and 17p13.1 and gain of 1q, are different from those found in ENKTL [37].
Although some treatment algorithms have been proposed for ENKTL and ANKL [43], there is no curative and uniformly accepted approach [44, 45].
Unlike in ANkL and our case, HSTCL cells are typified by medium-sized nuclei, loosely condensed chromatin, small inconspicuous nucleoli, and a rim of pale cytoplasm.
In comparison, ANKL is characterized by the presence of circulating neoplastic NK cells, with a range of appearances from cells that are slightly larger than large granular lymphocytes to cells with irregular nuclear contour, enlarged nuclei, immature chromatin pattern, and prominent nucleoli.
With the exception of lacking surface CD3 expression, ANKL cases can show an immunophenotype that is almost identical to that of HSTCL.
The circulating neoplastic cells of this case were blastlike with large irregular nuclear contour and contained scant azurophilic granules, findings commonly seen in ANKL. Also similar to NK cells, the cells lacked surface CD3 expression and expressed the NK-cell-associated markers CD56, CD16, and CD11B.