[Primary nasal natural killer/T-cell lymphomas: classification and clinicopathological features]

Nasal NK/T-cell lymphomas are rare malignancies in Europe or North America. Histological diagnosis is difficult, because tumors imbedded in large necrotic areas and neoplastic infiltrates may be admixed with small lymphocytes, plasma cells, eosinophils, and histiocytes, and thus the process could be misdiagnosed as chronic inflammation. Progression of the disease leads to septal perforation and may also result in destruction of the hard palate, and if left untreated it ends fatally. This introduced the term "lethal midline granuloma", a term which should not be used any more.

Clinical features, pathohistology, and current classification of primary nasal NK/T-cell lymphomas are described against the background of the recent literature and a case report.

Immunophenotyping is essential for the diagnosis. Tumor cells are uniformly infected by Epstein-Barr virus, which could be verified by EBER in situ hybridization. Immunohistochemically, tumor cells are positive for CD56, cytoplasmic CD3epsilon, and CD2 and they express cytotoxic molecules like granzyme B, TIA-1, GMP17, and perforin. Therapeutic options are radio- or radiochemotherapy. On average, 2- and 5-year survival rates of 50% are obtained in stages I and II. The prognosis of advanced tumor stages is very poor.

Immunohistochemical and molecular genetic early diagnosis is of crucial prognostic relevance.