SPP1 and neoplasm: Furthermore, three distinct patterns of OPN expression were observed in HCC tumor sections: type 1 revealed OPN expression in less than 10% tumor cells and was distributed across the bulk of the tumor; type 2 expression was characterized by localization to tumor cells at the edge of bulk tumor cells, which is the region that invades the capsule; the type 3 pattern was marked by constitutive OPN expression in almost all tumor cells.