If and how a tumor develops, depends in large part on its surroundings. While scientists agree on the importance of the tumor environment (TE), there is no consensus on how to define and spatially delineate it.

A new paper by Lucie Laplane, Dorothée Duluc, Nicolas Larmonier, Thomas Pradeu and Andreas Bikfalvi lays out six clearly defined layers that surround the tumor: (i) the tumor cell-only environment, (ii) the niche, and the (iii) confined, (iv) proximal, (v) peripheral, and (vi) organismal tumor environment. The authors show the different tumor-promoting or -suppressing mechanisms at work in the different layers and how they impact therapeutic approaches.