[Atypical clinicopathological features of monomorphic epitheliotropic intestinal T-cell lymphoma].

Objective: This study sought to examine the clinicopathological features of monomorphic epitheliotropic intestinal T-cell lymphoma (MEITL) and to discuss its differential diagnosis. Methods: A total of 36 MEITL cases, collected between June 2015 and January 2024 from the Fourth Affiliated Hospital of Soochow University and the First Affiliated Hospital, College of Medicine, Zhejiang University, were analyzed. Patients underwent immunohistochemistry, in situ hybridization for Epstein-Barr virus-encoded small RNA (EBER), and T-cell receptor (TCR) gene rearrangement testing. Clinical data, laboratory results, and follow-up information were collected for correlation analysis. Results: The cohort included 36 patients (20 males and 16 females) aged 17-76 years (median: 57 years). Tumors outside the intestine were observed in 22 cases (61%). A total of 32 patients (89%) underwent surgical intervention and/or chemotherapy, and one patient received auto-HSCT. The median follow-up duration was 11.5 months (range: 8-73 months), with a median overall survival of 6 months (range: 1-67 months) ; 34 patients died during the follow-up period. Morphologically, nine cases (25%) exhibited significant pleomorphism. Immunohistochemical analysis revealed that high expression levels of both P53 and c-Myc were correlated with atypical morphology (P=0.003 and P=0.016, respectively). Notably, patients with high P53 expression had significantly shorter survival times than those with low P53 expression (χ(2)=4.922, P=0.027), whereas survival did not differ significantly based on c-Myc expression levels (χ(2)=0.034, P=0.854). Furthermore, a PD-L1 CPS score ≥10 was observed in 22 cases (68.8%). Scattered EBER positivity in background cells was identified in four cases. All tested cases (17/17, 100.0%) showed clonal TCR gene rearrangements. Conclusions: MEITL is a rare but highly aggressive lymphoma with distinct clinical and pathological features. A subset of cases may exhibit atypical morphological patterns, complicating the diagnostic process. Improving awareness of this neoplasm is helpful for early and precise diagnosis as well as the estabolishment of novel therapy regimen.