OBJECTIVES: With oral antineoplastic agents (OAAs) becoming the mainstay of treatment for several cancer types, understanding risk factors for medication non-adherence is becoming increasingly important in oncology. Patient-reported outcome (PRO) instruments may provide valuable insight on barriers to medication adherence in the real world. This study sought to identify and describe key patient-reported risk factors for non-adherence measured in observational studies evaluating adherence with OAAs. METHODS: A targeted literature review was conducted to identify OAA adherence studies utilizing PROs and published between January 2004 and December 2014. Key data abstracted from each retained article included study design, cancer type, and all PRO instruments or study-specific questionnaires used. Domains measured by each PRO instrument and questionnaire were recorded to understand patient-reported risk factors measured. RESULTS: Of 100 articles reviewed, 11 studies met all study inclusion/exclusion criteria. Nine studies (82%) used at least one validated PRO instrument and 7 studies (64%) used at least one study-specific questionnaire to measure patient-reported risk factors for non-adherence. The most commonly used PRO instruments were the Beliefs about Medicines Questionnaire (BMQ; n=4) and the Satisfaction with Information about Medicines Scale (SIMS; n=3). Six studies (55%) used a validated PRO to measure health-related quality of life (HRQL); however, only the European Organization for Research and Treatment of Cancer Quality of Life Questionnaire (EORTC QLQ-C30) was used in more than one study. Overall, the most common domains measured by PRO instruments or questionnaires were knowledge about medication (n=7), beliefs about medication (n=6), HRQL (n=6), attitude toward disease (n=4), symptoms (n=3), and side effects (n=3). CONCLUSIONS: Risk factors for non-adherence are commonly measured by patient-report in observational studies evaluating adherence with OAAs. Further work is needed to clarify advantages and disadvantages of using specific PROs to measure relevant risk factors and determine if risk factors vary by cancer type.