Implications for Practice:
Outpatient palliative care clinics improve patient outcomes; however, it remains unclear who is appropriate for referral and what is the optimal timing. A better understanding of the referral criteria would help (a) referring clinicians to identify appropriate patients for palliative care interventions, (b) administrators to assess their programs with set benchmarks for quality improvement, (c) researchers to standardize inclusion criteria, and (d) policymakers to develop clinical care pathways and allocate appropriate resources. This systematic review identified 20 criteria including 6 recurrent themes for outpatient palliative cancer care referral. It represents the first step toward developing standardized referral criteria.