In looking for previous studies that best make the case for 3D cultures in drug discovery programs, the author had two criteria. First, the drug and target involved are either commercial or belong to a class of drugs from which commercial products exist. Second, the outcome of the drug interaction with the target in 3D cultures is directly linked to the success or failure in vivo, but such an outcome is absent in 2D cultures. Three groups of studies that meet the above criteria were found. The rst comes from Mina J. Bissell’s group at the Lawrence Berkeley National Laboratory, Berkeley, California, involving a β1-integrin monoclonal antibody that only successfully treated breast cancer cells in 3D cultures and tumors in vivo. The second comes from Peter Friedel’s group at the University of Würzburg, Würzburg, Germany, involving identi cation of alternative tumor cell migration after blocking the pericellular proteolysis; a potential partial explanation of the failure of metalloproteinase inhibitors in cancer therapy. The third comes from a study published almost a decade ago by Robert Kerbel’s group, at the Sunnybrook Health Science Center of the University of Toronto, in which the expression of drug resistance observed in vivo was fully recapitulated in vitro with multicellular spheroids. More detailed background of the target(s), drug(s), cell culture system(s), and results for each case are presented below.