OBJECTIVES:  Continuous suppression of the HER2+ (ErbB2+) receptor is an accepted treatment strategy for patients with HER2+ MBC. However, consideration of the evidence base is also important when identifying appropriate therapeutic options for patients who have progressed on trastuzumab (TZ). This study explores UK treatment patterns for women with HER2+ MBC who progress while on TZ, and have been previously treated with an anthracycline and a taxane (A&T). METHODS:  Case histories from 2815 women with MBC seen January 2006 to December 2007 were retrieved from the IMS Advanced Disease Analyzer database: 421 had received TZ in the metastatic setting. Changes in therapy were used as a proxy for disease progression; patients receiving TZ monotherapy within 28 days of ending a previous regimen were excluded from this definition to ensure that TZ use as a maintenance treatment was not inappropriately characterised as progression. Therapeutic regimens received post-progression were characterised for 98 patients who had progressed on TZ. Results were compared with a UK treatment survey completed by oncologists with a specialist interest in breast cancer (n=92).   RESULTS:  Of the 98 patients that progressed on TZ, 54 (55.1%) continued receiving a TZ-containing regimen, most commonly in combination with capecitabine (n=21; 21.4%) or vinorelbine (n=20; 20.4%).  Capecitabine monotherapy was also commonly used (n=31; 31.6%).  Re-challenge with a taxane was uncommon (n=1; 1.0%).  Major regimens received post-progression on TZ, as identified from case histories, agreed closely with results from the treatment survey. CONCLUSIONS: This study demonstrates that, despite the lack of a robust evidence base in this population, a high proportion of patients continue to receive a TZ-containing regimen post-progression. This highlights a clear need for evidence-based HER2 targeted therapy in a patient population where effective treatment options are limited.