Different infiltration patterns within the tumor microenvironment can identify mantle cell lymphoma patients with different clinical outcomes. Results from a pilot clinical-pathological study

Introduction Mantle Cell Lymphoma (MCL) is an aggressive B-cell neoplasm with well-defined histological features associated with prognosis. Early relapse recently proved to be associated with unfavorable outcomes. Although the intrinsic mechanisms underlying MCL pathogenesis have been elucidated, the extrinsic mechanisms regulated by tumor microenvironment (TME) are less known. Investigation of the crosstalk between MCL cells and their microenvironment is of preeminent importance to identify mechanisms of MCL earlier relapse and improve the effectiveness of treatment. Objectives To evaluate the histopathological features of relapsed/refractory (R/R) MCL cases, with focus on T-cells and macrophages infiltration. Correlation between TME, lymphoma characteristics and clinical outcome was then attempted. Methods This pilot study is part of the ongoing MANTLE-FIRST BIO study sponsored by Fondazione Italiana Linfomi (FIL). Thirty-eight histological samples of 28 R/R MCL patients (22 at diagnosis, 16 at relapse) from 3 Italian centers were evaluated by a consensus group of hemo-pathologists. Histopathological evaluation was performed on lymph nodes sections and included lymphoma cell morphology, patterns of growth, expression of CD20, CD5, Cyclin D1, Sox11, Bcl2, p53, c-Myc, IgM and Ki67 by immunohistochemistry. TME study included morphological scoring of histiocytic infiltration and quantitative evaluation of T-cells by CD3, CD4 and CD8 stains. Patients with clinical data available (N=11) were clinically classified as early (N=5) or late (N=6). progressors by the previously described threshold of 24 months (Progression of Disease, POD24). Association between pathological-defined groups and clinical parameters was performed using Fisher’s exact test and Mann-Whitney test. Paired data were compared by exact Wilcoxon signed-rank test and exact McNemar test. Results By comparing lymphoma samples at diagnosis and relapse, classic morphology and non-diffuse patterns of growth were most common in the first group. Samples at relapse were characterized by higher occurrence of diffuse expression of cyclin D1, higher Ki67, higher histocyte infiltration and lower CD4/CD8 T-cell ratio. In the early-POD group the most represented pattern was diffuse, instead, in the late-POD group nodular, diffuse, and combined patterns were equally represented. Cyclin D1 was mostly diffuse in early-POD, while occasionally modulated in late-POD. Ki67 was higher in early-POD. Bcl2 ad IgM were diffusely expressed in all cases; p53 positivity was higher in early-POD than in late-POD, while c-Myc was higher in late-POD. As regards TME, histocytes score was similar in the two groups (1+ in most cases). Interestingly, median CD3-cell infiltration was higher in early-POD than in late-POD and the CD4/CD8 ratio was lower in early-POD, indicating a higher prevalence of CD8-cells in patients that relapsed earlier. Due to the pilot nature of the study the number of cases analyzed were low and differences were not statistically significant. Though, the microenvironmental-based clustering demonstrated association with relevant clinical parameters such as POD. These findings indicate a role of T-cell infiltration in the biological mechanisms associated with MCL early relapse. Conclusions Our results suggest that individual differences in TME can reflect clinical outcomes and responses to therapy, thus highlighting the possible predictive significance of TME infiltration patterns in MCL. We thank FIL (PGR Ed. 2019) for funding support.