Natural killer-like T-cell lymphoma of the stomach.

We report the case of a 69-year-old white woman who developed a natural killer (NK)-like T-cell lymphoma involving primarily the stomach. The tumour consisted of large and pleomorphic lymphocytes infiltrating the gastric mucosa. Immunohistochemistry performed on paraffin sections showed the neoplastic cells to be CD3+, CD5-, CD8-, CD43+, CD45RO+, and CD57+. In addition, these cells also expressed HLA-DR, granzyme B, and, to a lesser extent, the CD30 activation marker. No pathologic features suggesting Helicobacter pylori, Epstein-Barr virus infection, or lymphocytic gastritis were found within adjacent normal mucosa. The patient had no previous history of coeliac disease, and her serology for H. pylori was negative. Since lymphomas are usually considered the neoplastic counterpart of normal lymphocytic subsets, it is possible that in this case the tumour cells originate from a distinct cytotoxic T-cell population normally present within the gastric mucosa. The pathogenesis of this highly unusual neoplasm, however, remains a mystery.