In both subgroups ARID1A alteration is associated with novel and distinctive histological features: (1) in β-catenin altered tumors, ARID1A loss correlates with high histologic grade, necrosis, tumor budding, TILs and high proliferative activity; (2) in the NSMP group, ARID1A mutation correlates with increased proliferative activity and, interestingly, it identified all NSMP with recurrent disease. This evidence concerns the gene ARID1A and neoplasm.