Surface CD3-negative monomorphic epitheliotropic intestinal T-cell lymphoma

Intestinal T/NK-cell lymphomas include enteropathy-associated T-cell lymphoma (EATL), monomorphic epitheliotropic intestinal T-cell lymphoma (MEITL), indolent T- cell lymphoproliferative disorders of the GI tract (ITCLPD), extranodal NK/T- cell lymphoma, nasal type (ENKTL), and intestinal T-cell lymphoma NOS ( ITCL-NOS). Here we describe a case of surface CD3negative MEITL. A 63-year-old Japanese female had a tumor located in the conglomerated ileum, which formed multiple mass lesions. The resected tissue showed a diffuse infiltration of monomorphic medium- sized lymphocytes with epitheliotropism. Flowcytometry using a fresh specimen of the tumor revealed positivity for CD7, CD8, CD38, and CD56, but not surface CD3. On immunohistochemistry, the tumor showed positivity for cytoplasmic CD3, CD8, CD56, TIA- 1, Granzyme B, and perforin. EBER with in situ hybridization was negative. Moreover, H3K36me3, which is negative in MEITL with SETD2-mutation, was positive. This is an important case of MEITL due to its oncogenesis.