OBJECTIVES: FDA and EMA have created guidelines for PRO label claims.   However, there have been few PRO-based label claims in oncology (Gnanasakthy, et al., 2012) since the release of the FDA guidelines.  The objective of this research was to explore factors that might predict regulatory success for PROs.  We developed a regulatory success gradient, and used factors based on literature review, expert interviews, and the FDA Guidances to predict success. METHODS: Using a case-control approach, 10 oncology medications with PRO labels came from two sources: 1) a review of PROs in oncology labels (Gondek et al, 2007), and 2) a proprietary database (http://www.mapi-prolabels.org/) containing a list of PRO-based labels.  Six controls were oncology medications with the same indication and mechanism of action, but without PRO data in the label.  Regulatory success was defined from none (no PRO in the label), through minimal, mild, and moderate, to great success (PRO labeling in the indication section).  Independent factors, derived from literature review, expert interviews, and the PRO Guidances, possibly related to regulatory success included conceptual fit, study quality, conformity to PRO Guidance (content validity), psychometrics score, and other PRO characteristics, were evaluated. RESULTS: No medication achieved great PRO labeling success.  Only three medications achieved moderate regulatory success, seven achieved mild, and five achieved minimal success.  None of the factors identified as potentially related to regulatory success were significantly correlated with it (Spearman correlations): Other PRO Characteristics (0.33), Conceptual Fit (0.09), Study Quality (-0.13), Psychometrics (-0.18), and Conformity to the PRO Guidance (0-0.02).  CONCLUSIONS: Despite widespread use of PROs in oncology, very few labels actually include PRO-based results, and furthermore, no medications achieved great success and only three moderate success in labeling.  Based on our regulatory success gradient, driving factors leading to regulatory success have yet to be identified.