Among the rare group of natural killer-cell (NK-cell) malignancies, there are two which primarily involve the peripheral blood and bone marrow: aggressive NK-cell leukemia (ANKL) and chronic lymphoproliferative disorder of NK-cells (CLPDNK). Distinguishing chronic lymphoproliferative disorder of natural killer (NK) cells from aggressive NK-cell leukemia is critical because they have distinct clinical course and management.
Mayo Clinic researchers, first author Min Shi, M.D., Ph.D., reported an unusual case of NK-cell neoplasm having an immunophenotype similar to that associated with ANKL but with clinical and laboratory features typical of the much more indolent CLPDNK. The case was published in Clinical Case Reports.
The patient is a 65-year-old Caucasian male with a 16-year history of leukopenia and neutropenia. He was completely asymptomatic, denying fevers, night sweats, or unexplained weight loss and had no documented history of neutropenic infection. An ultrasound revealed an enlarged spleen without focal masses. No hepatomegaly or lymphadenopathy was found. The patient had not received therapy for this condition.
The peripheral blood smear showed an increase in granular lymphocytes with bland nuclei and abundant pale-staining cytoplasm containing fine to coarse azurophilic granules. No nuclear atypia, such as enlargement, folding, or open chromatin, was noted. Peripheral blood flow cytometric immunophenotyping revealed significantly increased NK-cells.
The diagnosis of NK-cell leukemia is challenging for practicing pathologists because NK-cells lack a singular lineage defining antigen and are phenotypically similar to normal cytotoxic T-cells. Due to this, flow cytometric immunophenotyping is a primary laboratory tool as it allows for the accurate identification of NK-cells through combined assessment of antigens.
For more information, read the full case history and discussion.