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Although Gastrointestinal stromal tumors (GISTs) affect about 0.0014% of the population, GISTs smaller than 1cm (microGISTs) are detectable in about 20% to 30% of elderly individuals. This suggests that microGISTs likely represent premalignant precursors that evolve only in a minute fraction of cases toward overt GISTs. We sought histopathologic and molecular explanations for the infrequent clinical progression in small GISTs. To investigate the mechanisms of GIST progression and identify subsets with differential malignant potential, we carried out a thorough characterization of 170 GISTs< 2cm and compared their KIT/PDGFRA status with overt GISTs. The proliferation was lower in microGISTs compared with GISTs from 1 to 2cm (milliGISTs). In addition, microGISTs were more frequently incidental, gastric, spindle, showed an infiltrative growth pattern, a lower degree of cellularity, and abundant sclerosis. The …