6522 Background: The role of continued TRZ treatment (tx) after progression in 1st line tx in women with HER2+ metastatic breast cancer (Br Ca) is controversial. There are no completed controlled clinical trials (CTs) that establish a benefit to continued TRZ use, and these trials have been difficult to complete. We use the NCCN Outcomes Database project to describe the use of 2nd line TRZ at NCCN centers. Methods: Our sample is 165 women treated with TRZ based tx as their 1st line of tx for newly diagnosed metastatic or relapsed HER2+ BrCa at 8 NCCN centers; who were treated between July 1997 and December 2004; and who had at least 450 days of follow up. Reason for tx changes were recorded by individual NCCN centers. In addition, women who were on single agent TRZ but later started chemotherapy or hormonal therapy were considered to have progressed. We also recorded the number of women who received TRZ on CTs. We used logistic regression to determine if age, sites of metastatic disease, year of diagnosis or NCCN Center were associated with a higher likelihood of receiving continued TRZ after disease progression. Results: See Table. 56 women discontinued 1st line tx due to progression and 6 pts discontinued for unknown reasons. Of these 62 pts, 46 (74%), continued TRZ. No prespecified candidate predictor variable was associated with 2nd line TRZ beyond progression. Of the 103 remaining of women, 35 (21.2%) discontinued 1st line tx for toxicity, 12 (7.3%) for other reasons and 46 (27.9%) for a planned treatment break. Conclusions: In these academic centers, despite the absence of evidence supporting the practice, 74% of patients who progressed while receiving TRZ continued TRZ as part of 2nd line therapy. Only 20% of these were treated on a clinical trial. Randomized CTs of new targeted therapies for all disease sites are needed to establish the role of treatment beyond progression Use of Trastuzumab (TRZ) in the NCCN N (%) Median duration of treatment in months (range) N (%) treated on a TRZ based clinical trial 1st line TRZ based tx (N=165) 5.62 (0*-37.9) 49 (29.7) Chemotherapy ± hormonal therapy and TRZ 150 (90.9) 5.39 (0*-29.2) 48 (32) Hormonal Therapy and TRZ 5 (3.0) 12.62 (0.8–37.9) 0 (0) TRZ alone 10 (6.0) 9.82 (2.9–30.1) 1 (10) 2nd TRZ based tx after progression (N=46)** 5.04 (0.5–40.3) 9 (19.6) Chemotherapy ± hormonal therapy and TRZ 31 (67.4) 4.80 (0.5–40.3) 6 (18.6) Hormonal Therapy and TRZ 3 (6.5) 2.7 (2.7–7.2) 1 (33.3) TRZ alone 12 (26.1) 7.95 (1.9–36.8) 2 (16.7) * Patient had 1-day course because of toxicity. ** Of 66 patients who stopped 1st line tx for progression or unknown reasons No significant financial relationships to disclose.