[Monomorphic epitheliotropic intestinal T-cell lymphoma: a clinicopathological analysis of twelve cases].

Objective: To investigate the clinicopathological features, diagnosis and differential diagnosis of monomorphic epitheliotropic intestinal T-cell lymphoma (MEITL). Methods: A total of 12 specimens were collected, which were surgically resected and verified as MEITL by postoperative pathology, immumohistochemical staining and gene rearrangement at the First Affiliated Hospital of Nanjing Medical University from 2012 to 2018, and all of these had complete clinical and pathological data. The MEITL cases were reviewed to compare the clinicopathological characteristics, including morphologic and immunophenotypic features and followed up by telephone and clinic visit. Results: All the cases were diagnosed with MEITL. There were 8 males and 4 females. Male to female ratio was 2∶1, at a median age of 54 years. The sites of involvement included jejunum (4 cases), ileum (5 cases), duodenum (1 case), ileocecal junction (1 case) and rectum (1 case). The neoplastic cells were monotonous of small to intermediate cells in size with round to slightly irregular nuclei in 11 cases. The immunophenotyping showed that CD3 (12/12), CD8 (11/12), CD43 (11/12), CD56 (11/12), TIA-1 (12/12) were positive; CD5 (12/12), Gran B (9/12), and perforin (7/12) were negative. Two cases aberrantly expressed the B-cell marker CD20. A high proliferation index was demonstrated by Ki-67 immunostaining. In situ hybridization for EBER was all negative(12/12). The whole exome sequencing(WES) mutational landscape of MEITL was remarkably homogeneous, showing significantly enriched clusters among histone modifier genes, JAK-STAT and MAPK-signal pathways. Histonelysine N-methytransferase SETD2 gene was mutated in 2/4 tumors. All the patients analyzed harbored at least one mutation in the JAK-STAT signal pathway, including STAT5B (2/4), JAK3 (3/4) and STAT5A (2/4). Furthermore, frequent alterations (TP53) were observed in the MAPK pathway in 3/4 of MEITL cases. The CNV analysis derived from WES data identified multiple regions of frequent gains and losses. In particular, gains in 1q, 7q and 9q, and recurrent losses involving 7p and 8p were observed. Conclusions: MEITL is a rare and aggressive type of extranodal T-cell lymphoma. The differential diagnosis of MEITL includes EATL, extranodal NT/T-cell lymphoma and other types of PTCL. Diagnosis should be correlated to clinical symptoms while the final diagnosis is mainly based on the pathological features, immunophenotypes and genetic testing.