We consider a multistage cancer model in which cells are arranged in a $d$-dimensional integer lattice. Starting with all wild-type cells, we prove results about the distribution of the first time when two neutral mutations have accumulated in some cell in dimensions $d\ge2$, extending work done by Komarova [Genetics 166 (2004) 1571–1579] for $d=1$.
"Spatial Moran models I. Stochastic tunneling in the neutral case." Ann. Appl. Probab. 25 (1) 104 - 115, February 2015. https://doi.org/10.1214/13-AAP989