Although comparative effectiveness trials and nationally recognized clinical guidelines offer substantial guidance
about ideal patient treatment, we remain largely uninformed about the patterns of care seen in everyday clinical
practice. To address this gap in knowledge, we looked at registry-based data on breast cancer care at two
neighboring healthcare institutions with a specific focus on whether organizational boundaries determine the
physicians that a patient will see. From an initial patient-oriented data set, we developed a social network of
physicians, modeling their interactions over the course of the provided treatments. Applying a mixture of visual and
quantitative analyses to this network, we found evidence for strong intra-institutional ties and poignantly weak
connections to physicians operating out of other healthcare centers.