OBJECTIVES: Eribulin mesylate is a microtubule inhibitor FDA approved in 2010 for patients with MBC after treatment with at least two prior chemotherapeutic regimens.  This study utilized real-world claims data to evaluate the utilization of eribulin mesylate by line of therapy at two and five years post launch to determine the degree to which patterns of utilization by line of therapy and payer type change over time without an associated change in labeling.  METHODS: Using data from the Cardinal Health Specialty Solutions Revenue Cycle Management medical claims database, patients who received 2 or more eribulin administrations and completed therapy between May 2014 and April 2015 were included in the current analyses (n=368). The distribution of this study group was compared to a similar patient population identified as having completed therapy between April 2011 and March 2012 (n=424). Patients were assigned line of therapy for each treatment regimen received during their entire MBC treatment history. Distribution of patients by payer type (Medicare, Medicaid, Commercial) was also evaluated.  Data was analyzed using Pearson chi-square. RESULTS: An analysis of patient distribution revealed the share of eribuilin treated patients that received treatment in first or second line in the 2015 study cohort (42.1%) was significantly higher than the share reported in the 2012 cohort (32.8%) (p=0.007). The share of Medicare patients among the first and second line treatment group increased from 2012 (32.5%) to 2015 (44.5%) (p=0.044). CONCLUSIONS: Eribulin mesylate utilization in earlier lines of treatment has increased over time possibly due to greater familiarity among MBC treating providers. In addition, this increase in earlier use of eribulin mesylate has come to a greater degree among Medicare patients, possibly highlighting more stringent controls among commercial payers.