MALIGNANT LYMPHOMA, EXTRANODAL NK/T-CELL LYMPHOMA, NASAL TYPE, MOST LIKELY OF NATURAL KILLER CELL ORIGIN.
Extranodal NK/T-cell lymphoma, nasal type, is a rare disease in the United States, but more prevalent in Asia, Mexico and Central and South America (1, 2). While most cases appear to be NK-cell in origin, some cases may be composed of cytotoxic T cells (1, 2). The most common site is the nasal cavities or paranasal sinuses. Other sites may include skin, gastrointestinal tract, testis, kidney, upper respiratory tract and rarely the eye/orbit (1, 2). Clinical presentation varies depending on the primary sites of involvement. Commonly patients present with a nasal mass with bleeding and local bony destruction. Rarely they may present with skin ulcer or GI perforation if these sites are primarily involved (1, 3). About 10-20% of patients presenting with nasal NK/T-cell lymphoma may also have skin involvement at same time (3).
Although extranodal NK/T-cell lymphoma, nasal type, is found in various places, they often bear very similar histological features throughout (1). Characteristic features include a prominent but not invariable angiocentric/angiodestructive growth pattern, extensive mucosa ulceration, coagulative necrosis and pseudoepitheliomatous hyperplasia. Often admixed are prominent inflammatory cells including plasma cells, histocytes and often eosinophils. Tumor cells vary greatly in size, but, in most cases, they are composed of medium-sized cells or a mixture of small and large cells. They often have granular or vesicular nuclei with irregular nuclear contour and inconspicuous nucleoli and moderate pale to clear cytoplasm. Mitosis is easily found.
The most typical immunophenotype of extranodal NK/T-cell lymphoma is: CD2+, CD56+, surface CD3-, cytoplasmic CD3+, cytotoxic granules such as TIA-1 + and germline TCR. The expression of CD8 and CD7 is variable. In some cases it may be CD56- and TCR rearranged cytotoxic T-cell lymphoma (1). The EBV positivity is seen in about 80-100% of cases (3). No specific cytogenetic aberrations have yet been found associated with this lymphoma. The most common ones reported are del(6)(q21q25) or i(6)(p10), but whether these are a primary event or a progression-associated one is not clear (1).
The prognosis of extranodal NK/T-cell lymphoma is variable. Some patients respond well to chemotherapy such as CHOP combined with local radiation, achieving complete remission and others die of disseminated disease despite aggressive therapy (1, 4). The cytological features have not shown consistent correlation with its prognosis (1, 5). Further subtyping of this lymphoma based on the gene expression profile may be necessary to reflect its clinical behavior.
Contributed by Zhengbin Lu, MD