SOS1 and cancer: Using two distinct measures of pharmacologic synergy, we demonstrate that SOS1 inhibition using BAY-293 synergizes with osimertinib only under 3D spheroid culture conditions, and in doing so add to the growing evidence that pharmacologic assessment of novel therapeutics designed to treat cancer must be performed under 3D culture conditions (Ekert et al., 2014; Sheffels et al., 2018; Nunes et al., 2019; Janes et al., 2018; Jacobi et al., 2017).