OPRPN and neoplasm: The difference to the 2D assay is potentially becausethe positive effects of PROL1 on cell motility and migration areonly observed when cells face a environment more akin to an environment present in atumor, in vivo, and the 3D spheroid assay is generally considered a better tool tomodel the phenotypic and cellular heterogeneity, as well as microenvironmentalaspects, of tumor growth in vivo [49].