Breast cancer affects 1 in 8 women, more than 300,000 new cases every year. Surgery is the most effective approach to curing breast cancer. Minimally invasive surgery is recommended but optional. Lumpectomies have a re-excision rate of 25%. Here we introduced a method for simulating the displacement and deformation of the breast, and underlying structures, during the prone-to-supine transition, as means of creating accurate 3D models for surgical planning.