title: Linking electronic health records to better understand breast cancer patient pathways within and between two health systems.
abstract: BACKGROUND
  In a fragmented health care system, research can be challenging when one seeks to follow cancer patients as they seek care which can continue for months or years and may reflect many physician and patient decisions. Claims data track patients, but lack clinical detail. Linking routine electronic health record (EHR) data with clinical registry data allows one to gain a more complete picture of the patient journey through a cancer care episode. However, valid analytical approaches to examining care trajectories must be longitudinal and account for the dynamic nature of what is "seen" in the EHR.
  
  
  METHODS
  The Oncoshare database combines clinical detail from the California Cancer Registry and EHR data from two large health care organizations in the same catchment area-a multisite community practice and an academic medical center-for all women treated in either organization for breast cancer from 2000 to 2012. We classified EHR encounters data according to typical periods of the cancer care episode (screening, diagnosis, treatment) and posttreatment surveillance, as well as by facility used to better characterize patterns of care for patients seen at both organizations.
  
  
  RESULTS
  We identified a "treated" cohort consisting of women receiving interventions for their initial cancer diagnosis, and classified their encounters over time across multiple dimensions (type of care, provider of care, and timing of care with respect to their cancer diagnosis). Forty-three percent of the patients were treated at the academic center only, 42 percent at the community center only, and 16 percent of the patients obtained care at both health care organizations. Compared to women seen at only one organization, the last group had similar-length initial care episodes, but more frequently had multiple episodes and longer observation periods.
  
  
  CONCLUSIONS
  Linking EHR data from neighboring systems can enhance our information on care trajectories, but careful consideration of the complexity of the treatment process and data generating mechanisms is necessary to make valid inferences.
  If analyzed as a timeline, and with careful characterization of diagnostic tests, surgical interventions, and type and frequency of physician encounters, the pathways taken by women through their breast cancer episode may lead to better understanding of patient decisions.
authors.affiliation: Palo Alto Medical Foundation Research Institute.
authors.forename: Caroline A
authors.initials: CA
authors.lastname: Thompson
authors.affiliation: Stanford University School of Medicine.
authors.forename: Allison W
authors.initials: AW
authors.lastname: Kurian
authors.affiliation: Palo Alto Medical Foundation Research Institute.
authors.forename: Harold S
authors.initials: HS
authors.lastname: Luft
keywords: 2014 EDM Forum Symposium; Data Use and Quality; Methods