Final considerations and perspectives
Even though 3D culturing is clearly incapable of replacing other current research types, they might continue to replace some unnecessary animal experimentation, as well as improve monolayer cultures. It is not even recommended or expected that 3D models substitute all other research types, but in regard to animal testing, they come in hand for the 3 Rs: Reduction, Refinement, Replacement. The concept, postulated in 1959 by Russel and Burch, is still very pertinent, and proposes the need for alternative methods that present at least one of the following: Reduction in the total number of animals used; Refinement of experiments that endure pain or suffering; Replacement of experiments that can be performed without animals with the same representability (Costa et al., 2018; Kirk, 2018; Russell and Burch, 1959). Both spheroids and organoids represent, in this way, a further step in replicating organ characteristics in absence of animal suffering and with small ethic concerns, and promising candidates as realistic models that will thrive us to the medicine of the XXI century.