April 2009
Written by Peter M. Banks, M.D., Director of Hematopathology, Carolinas Medical Center, Charlotte, North Carolina.

Diagnosis
NK-cell lymphoblastic lymphoma.

Submitting Pathologist
James Siebert, M.D., Department of Pathology, St. Francis Medical Center, Peoria, Illinois.

Case History
This 56 year old male suffered progressive thrombocytopenia and developed bilateral inguinal and pelvic-retroperitoneal lymphadenopathy. A diagnosis of a myeloprolierative disorder had reportedly been made 6 months earlier.

Microscopy
Sections of lymph node show a malignant, diffuse, effacing process which has replaced almost the entire substance of the node, with the exception of a few small islands of residual benign small lymphocytic cellularity (see Figure 1).

At high magnification the neoplastic process can be seen to be composed of medium-sized cells with delicate chromatin and creased nuclear membranes (see Figure 2).
Bone marrow biopsy showed clusters of abnormal cells identical in appearance to those seen in the lymph node, and the apirate smear preparations displayed an abnormal population of cells with abundant pale slightly granular cytoplasm and delicate chromatin with small nucleoli (see Figure 3).

Ancillary Studies
Flow cytometry was performed on both lymph node and marrow samplings, demonstrated an abnormal population of cells positive only for CD2, CD56, CD38 and CD33, whereas by contrast these cells were only faintly positive for CD4 and negative for CD3, CD5. Tumor cells failed to express all other tested B-cell and myeloid markers, including CD34. Paraffin section immunohistochemical studies showed the tumor cells to be positive for CD56, CD45 and CD43 (see Figure 4). There was extremely weak, variable staining for terminal transferase They were negative for CD34, CD117 and myeloperoxidase.

Discussion
To describe this form of hematolymphoid malignancy as rare would be an understatement. It has only just debuted as a provisional entity in the new (Fourth Edition) WHO classification in the short chapter transitioning between the myeloid and lymphoid sections for "neoplasms of ambiguous lineage" (1).

This tumor shows cellular morphologic features intermediate between lymphoblasts and myeloid blasts. It is essentially negative for markers specific for T- and B-cell lymphoid differentiation and is strongly positive for CD56, a marker typical but not specific for NK-cells. It does express one myeloid marker, namely, CD33. However, over time it has been noted that NK-cells share a common myeloid stem cell, as is more commonly observed in cases of aggressive NK-cell leukemia (2).

References

1. Swerdlow S, Campo E, Harris N, et al., (Eds.)
   WHO Classification of Tumours of Haematopoietic and Lymphoid Tissues, 4th ed. Lyon, France, IARC Press, 2008:p. 155.
2. Swerdlow S, Campo E, Harris N, et al., (Eds.)
   WHO Classification of Tumours of Haematopoietic and Lymphoid Tissues, 4th ed. Lyon, France, IARC Press, 2008:p276-277.

» Return to the Top »