“…Analytical setting and current challenges. A promising framework for analysis of structured population systems is offered by the recently developed mathematical theory of PDE models defined in the space of Radon measures [1,2,3,6,15,16,17,18,23,24,25,45,46,47] and a related approach of measure differential equations [13,5,37,39]. To account for both discrete and continuous cell distributions as well as a possible non-Euclidean structure of the state space such as graphs, one needs to go beyond R d and define models on a reasonably generic metric space.…”