The International Consortium for Health Outcomes Measurement (ICHOM) aims to unlock the potential of value-based healthcare by defining global sets of health-outcomes measurements that involve provider observations as well as patient reported outcomes, and that drive adoption, reporting, and benchmarking of these measures worldwide to create better health outcomes for all stakeholders.   So far, sets for close to 40 health conditions have been defined by bringing together global teams of patient advocates, healthcare professionals and researchers, as described at https://www.ichom.org/standard-sets/ . More sets are under development to further increase the coverage of diseases and conditions.   To facilitate adoption and implementation of these ICHOM health-outcomes measurement sets in healthcare IT systems requires them to be published in an interoperable, open-standards-based machine-readable form. This will facilitate the semantically-interoperability collection of the required measurements along the patient care pathway, as well as the subsequent outcomes reporting based on these measurements. To this end, ICHOM would like to create and publish FHIR Implementation Guides for representing and exchanging their health-outcomes measurement sets. The international scope of ICHOM standard sets, including the one under scope for this proposal (Breast Cancer), will enable global usage, adoption, and implementation in clinical practice.   To create optimal alignment and reuse with existing initiatives in HL7 (such as the Breast Cancer Modeling, CREDS, mCODE, Outcome Criteria Framework, Quality Reporting Document Architecture, and Care Plan Project, etc. ) we propose this as an HL7 FHIR project under the guidance of the relevant HL7 FHIR working groups.   The proposed approach is to start with the health-outcomes measurement set for specifically Breast Cancer, and to leverage the learnings and reuse the FHIR IG results of this first condition to sequentially pick up additional conditions to build out a set of (dependent) FHIR IGs, including shared commonalities in a base IG.   The deliverables will include one or more FHIR Implementation Guides describing the representation of the ICHOM health-outcomes measurement sets, including: o What to measure and to report: FHIR profiles, including events, patient reported outcomes, observations, conditions, reports, etc. and associated value sets and code systems (leveraging global, standardized terminologies incl. SNOMED and LOINC) o When to measure and to report: Scheduling information about which measurement needs to be collected at which point in time for a patient (at diagnosis, during admissions, during release from the hospital, 3 months after treatment, etc.), using workflow constructs.