High grade malignant lymphoma with clinical characteristics and immunophenotype of natural killer cells

The malignant proliferation of natural killer (NK) cells which are morphologically characterized as large granular lymphocytes (LGL) is a well known clinical entity which was named after its morphological appearance as LGL-leukemia/lymphoma. Similar to non-malignant NK-cells, these tumors can be divided into those which express the CD3-T-cell receptor complex and those which do not. The CD3-positive type of LGL-leukemia is immunophenotypologically characterized by the expression of CD16, and variably CD 56 and CD 57, and generally follows a more indolent course. In contrast, malignant proliferations of CD3-negative LGL express either CD16 or CD 56, and only occasionally CD 57 on their cell surface. Clinically, CD3-negative NK-lymphomas tend to progress rapidly. We report here the case of a high grade malignant lymphoma which was characterized by an immunophenotype typical for CD3-negative NK-cells (CD2+, CD3-, CD16+, CD56(+), CD57-). The disease proved to be rapidly fatal despite aggressive chemotherapy. Interestingly, the patient suffered from a high turn over pancytopenia, which also characterizes NK-cell leukemias/lymphomas of the LGL-type. However, our patient's lymphatic cells appeared highly immature, and cytoplasmic granules, characteristic for LGL-cells, could not be discerned either microscopically or electronmicroscopically. Furthermore, the malignant lymphatic population had the T-cell receptor beta-chain rearranged. We therefore concluded that our patient might have suffered from a malignant proliferation of a putative precursor cell intermediate between T-cells and NK-cells.