This application note demonstrates the use of standardized, cryopreserved 3D human tumor spheroids for robust and predictive small-molecule testing in oncology. Due to their size and shape we also use the term microtissues for them. Using a panel of clinically relevant chemotherapeutic agents, we evaluate compound efficacy across three well-characterized human cancer cell lines, A549 (lung carcinoma), HCT116 (colorectal carcinoma), and T-47D (breast carcinoma), each of which is known to exhibit markedly different therapeutic responses in conventional 2D monolayer cultures compared with 3D tumor models.