The present invention refers to a process for preparing a three-dimensional tumor model having a core-shell structure using bioprinting techniques leading to tumor models capable of better reproducing the physiopathological complexity of real tumors, mimicking the tumor microenvironment and the original tumor tissue extracellular matrix. The process is based on the use of dECM (decellularized extracellular matrix) bioinks but with the particularity that no exogenous biopolymers that modify the rheological properties to improve printability are needed. The absence of rheological modifiers in the bioinks avoids any kind of physical or biochemical interference in the tumor model so obtained.