Agent-based simulation of ductal carcinoma in situ (DCIS), a type of breast cancer that is constrained to growth in the breast duct lumen by a basement membrane. Shown here: a simulation of 45 days’ growth in a 1.5 mm length of duct. The mechanical and population dynamic parameters have been calibrated to patient-specific immunohistochemistry and other histologic measurements. Dark circles: cell nuclei Green cells: proliferating cells (Ki-67 positive; S, G2, M, or G1) Red cells: apoptosis cells (cleaved Caspase-3 positive) Pale blue cells: quiescent cells (G0) Dark grey cells: necrotic cells prior to lysis Debris in centre of duct: necrotic cellular debris Red dots in centre of duct: clinically-detectable microcalcifications Method: Agent-based, lattice-free model. Cell velocities determined by balance of adhesive and repulsive forces. Each cell has a phenotypic state governed by stochastic processes derived from nonhomogeneous Poisson processes. Source: Macklin et al. 2011 in review. See: www.MathCancer.org Note: This is an update of the earlier animation at www.youtube.com