Histological analysis of invasive glioblastoma organoids embedded in a 3D collagen matrix

Organoids are unique tools to mimic how tumors evolve in a 3D environment. Here, we present a protocol to embed spheroids invading a 3D matrix into a paraffin mold. We describe steps for preparing spheroids, collagen and agarose inclusion, and paraffinization. We then detail procedures for sectioning, staining, and visualization. This protocol allows histological identification of markers expressed in cells escaping the tumor. For complete details on the use and execution of this protocol, please refer to Guyon et al. (2022).¹.