A 41-year-old man presented with a 1-month history of diarrhea and new-onset abdominal pain. Abdominal computed tomography revealed an extramural tumor of the small intestine with a diameter of 5 cm and perforation. Histopathologic examination of the tumor revealed intestinal mucosa that was diffusely infiltrated by monomorphic, medium-size lymphocytes with epitheliotropism (panels A-B; hematoxylin and eosin stain, original magnification ×100 [A], ×600 [B]). The immunophenotype was CD3⁺/CD4^–/CD8⁺/CD56⁺ (panels C-F; original magnification ×400) and Epstein-Barr virus-encoded RNA in situ hybridization–negative. Monomorphic epitheliotropic intestinal T-cell lymphoma (MEITL) was diagnosed. Cyclophosphamide, doxorubicin, vincristine, and prednisone (CHOP) and 3 cycles of ifosfamide, carboplatin, and etoposide (ICE) chemotherapy resulted in complete remission (CR). However, the patient developed right facial paralysis after ICE chemotherapy. Disseminated hyperintense lesions were identified by fluid-attenuated inversion recovery magnetic resonance imaging of the brain (indicated by arrows in panels G and H). A cytospin preparation derived from cerebrospinal fluid revealed numerous medium-size atypical cells with large irregular nuclei (panel I; Giemsa stain, original magnification ×400). Flow cytometry showed that the cells were CD3⁺/CD4^–/CD8⁺/CD56⁺/TCRγδ⁺ (panel J). The patient received repeated intrathecal chemotherapy and high-dose chemotherapy followed by autologous peripheral blood stem cell transplantation and achieved CR once again.

The optimal management of MEITL remains undetermined and the role of central nervous system prophylaxis in peripheral T-cell lymphoma remains controversial. Recent studies of patients with MEITL have uncovered SETD2 inactivation, which correlates with defective H3K36me3. The finding that WEE1 inhibition selectively targets H3K36me3-deficient cancer cells might provide a promising therapeutic option for MEITL.