Case 26. Extranodal NK/T-Cell lymphoma, extra-nasal type

NK/T-cell lymphomas are extremely rare lymphomas in the western world. The population of CD3+CD56+ NK/T-cells that seems to be the progenitor cells for those types of lymphomas is not homogeneous, which may explain the reason for polymorphic presentation. Several functionally distinct NK/T-cell subsets diverge after their development in the thymus. Organ-specific antigen-presenting cells may modulate NK/T-cell function and post-thymic development. The organs with the highest content of NK/T cells are tonsils, lymph nodes, spleen, skin, testis, and stomach. Not surprisingly, those are the places of the most frequent localization of NK/T-cell lymphoma. The Waldeyer’s tonsillar ring is involved most commonly. The patient sometimes may present with a single cutaneous nodule, but the asymptomatic nasal involvement could be detected on PET/CT frequently, still placing the patient into “the nasal” category. Extranasal presentation comprises around 20% of all cases and most likely arises from the dermal NK/T cells in contrast to tonsillar NK/T cells in “the nasal” cases. Unusual cases of such rare cancer are characterized by the unusual expression of non-NK/T-cell markers and rare morphologic presentations. The aberrant expression of γδ TCR on EBV+ CD56+ cells is still a matter of debate of appropriate classificational categorization. Despite semantics, the prognosis is universally gravid.