Endoscopically, eight of 15 MEITL lesions (53.3%) and eight of 10 GI EBV + TNKCL (80%) showed the ulcero-infiltrative type in 42 GI TNKCL . Infiltrating and superficial/erosive type lesions were rarely found in each of the above histological groups. Another study demonstrated that nine intestinal EBV + CD8+/−, CD56+/− TNKCL patients showed ulcerative (n = 5) and protruding (n = 4) type lesions . Furthermore, 34 of 47 GI EBV + CD56 + TNKCL patients (72.3%) frequently showed multiple ulcerative lesions . In the current study, the ulcerative type was frequently encountered in four of seven other group patients (57%), in which two EBV + TNKCL were included. Six MEITL patients (67%) and five ATLL (46%) mainly showed the diffuse infiltrating type. Although ulcerating and polypoid type lesions were also found in resting MEITL and ATLL patients, the diffuse infiltrating type was a frequently encountered characteristic of colorectal MEITL and ATLL, which was different from that of EBV + TNKCL as well as B-cell lymphoma. Further detailed studies are necessary to clarify the endoscopic difference among MEITL, ATLL and GI EBV + TNKCL.
Small intestinal MEITL mostly showed intramucosal spreading of lymphoma cells with neoplastic CD103 + and CD8 + T-IELs . It was reported that lymphoma cells in 21 of 31MEITL (68%) as well as 31 of 56 GI ATLL patients (55%) showed expression of CD103 homing receptor of T-IELs, and ATLL had similar histopathological characteristics to MEITL with respect to increased atypical and reactive T-IELs . The endoscopic findings of MEITL have been reported as edematous mucosa with mosaic and diffuse mucosal thickening patterns, and shallow ulceration, as well as ulcerative type tumors in the small intestine . The endoscopic findings of GI-involved acute type ATLL showed superficial spreading-type lesions (equal to the diffuse infiltrating type) in 12 of 23 lesions (52%) . In the current study, more than two colorectal lymphomatous lesions were frequently found in MEITL patients (78%) and ATLL (64%). Histologically, increased atypical T-IELs were found in MEITL patients (88%) and ATLL (60%). Although MEITL and GI ATLL showed distinct disease entities, the endoscopic and pathological characteristics of colorectal MEITL were similar to those of ATLL.
A multicenter study from the Asia Lymphoma Study Group identified 38 MEITL patients, and the involved sites were the small intestine and stomach (5%), small intestine (63%), small and large intestine (16%), and large intestine (18%) . MEITL can discontinuously expand into the mucosa along the entire GI tract. Aoyama et al. reported a primary colonic MEITL patient with Lugano clinical stage I, having mucosal edema and multiple ulcers in the transverse, splenic flexure, and sigmoid colon . The current study also demonstrated that three MEITL patients (33%) had primarily presenting colorectal lesions. Endoscopically, six MEITL patients (67%) showed diffuse infiltrating type with more than two lymphomatous lesions in the whole colorectum. A previous study reported two colonic MEITL patients with clinicopathological features that mimicked those of ulcerative colitis and lymphocytic colitis, and the latter had a history of 'lymphocytic colitis' before 6 months . Although collagenous sprue, microscopic (lymphocytic and collagenous) colitis, and celiac disease show distinct clinical entities, these diseases reveal similar features of colitis with an increase in T-IELs [25, 26]. Five examined MEITL patients (56%) had features of lymphocytic proctocolitis with reactive small T-IELs, and the findings were almost similar to lymphocytic colitis, in which more than 20 IELs per 100 epithelial cells and no or few distorted crypts were detected . The features of lymphocytic proctocolitis may be characteristic of background mucosa in colorectal and other GI MEITL. Cumulative studies are necessary to clarify the relationship between lymphocytic proctocolitis and MEITL.
The prognosis of GI TNKCL patients is worse, and 1- and 3-year OS rates were 57% and 26%, respectively, in 42 intestinal MEITL patients . Among them, OS of MEITL patients with Lugano clinical stages I, II1, and II2 was 18.8 months, which was significantly better than 4.9 months in stages IIE and IV (P = 0.01). The Lugano stage as well as the performance scales were important prognostic factors. Clinical stage in 55 GI EBV + TNKCL patients and 61 GI-involved ATLL were also indicated as a significant prognostic factor (P < 0.001 and P = 0.017, respectively) [8, 22]. In the current study, only five of 27 colorectal TNKCL patients (19%) were found with stage I and II1, and 50% OS was more than 240 months. The major symptom of examined colorectal TNKCL patients was chronic diarrhea. Thus. the clinical symptoms as well as the features of lymphocytic proctocolitis with CD8 + T-IELs may be important in detecting the early stages of colorectal TNKCL.