Ductal carcinoma in situ (DCIS) is the most commonly diagnosed form of non-invasive breast cancer, constituting 20% of all new breast cancer cases in the United States. Although non-invasive, DCIS is usually treated surgically through resection. Interestingly, long-term survival studies have shown that patient survival rates are not significantly impacted by the type or resection, indicating that increased breast conservation through minimized surgical resection may indeed be possible. This requires a greater understanding of disease development, so that clinicians may more accurately determine surgical margins which minimize patient impact while maintaining survival rates. To this end, we have developed a three-dimensional, lattice-free multiscale agent based model of DCIS designed to help quantify ductal invasion rates, in order to allow clinicians to better estimate disease age and extent of invasion, and to predict surgical margins based on parameters obtainable from non-invasive testing (i.e., mammography). Here, we present the model development to date, and discuss some preliminary results.