[Lani]

As I understand it it was used in those so advanced they preferred not to have anymore chemotherapy, so in many of these patients it may have been an "uphill" battle for ANY medication to prove its efficacy:

1: J Clin Oncol. 2002 Feb 1;20(3):719-26. Links
Efficacy and safety of trastuzumab as a single agent in first-line treatment of HER2-overexpressing metastatic breast cancer.

Vogel CL,
Cobleigh MA,
Tripathy D,
Gutheil JC,
Harris LN,
Fehrenbacher L,
Slamon DJ,
Murphy M,
Novotny WF,
Burchmore M,
Shak S,
Stewart SJ,
Press M.
University of Miami School of Medicine, Comprehensive Cancer Research Group Inc, and Columbia Cancer Research Network of Florida, Miami, FL, USA.
PURPOSE: To evaluate the efficacy and safety of first-line, single-agent trastuzumab in women with HER2-overexpressing metastatic breast cancer. PATIENTS AND METHODS: One hundred fourteen women with HER2-overexpressing metastatic breast cancer were randomized to receive first-line treatment with trastuzumab 4 mg/kg loading dose, followed by 2 mg/kg weekly, or a higher 8 mg/kg loading dose, followed by 4 mg/kg weekly. RESULTS: The objective response rate was 26% (95% confidence interval [CI], 18.2% to 34.4%), with seven complete and 23 partial responses. Response rates in 111 assessable patients with 3+ and 2+ HER2 overexpression by immunohistochemistry (IHC) were 35% (95% CI, 24.4% to 44.7%) and none (95% CI, 0% to 15.5%), respectively. The clinical benefit rates in assessable patients with 3+ and 2+ HER2 overexpression were 48% and 7%, respectively. The response rates in 108 assessable patients with and without HER2 gene amplification by fluorescence in situ hybridization (FISH) analysis were 34% (95% CI, 23.9% to 45.7%) and 7% (95% CI, 0.8% to 22.8%), respectively. Seventeen (57%) of 30 patients with an objective response and 22 (51%) of 43 patients with clinical benefit had not experienced disease progression at follow-up at 12 months or later. The most common treatment-related adverse events were chills (25% of patients), asthenia (23%), fever (22%), pain (18%), and nausea (14%). Cardiac dysfunction occurred in two patients (2%); both had histories of cardiac disease and did not require additional intervention after discontinuation of trastuzumab. There was no clear evidence of a dose-response relationship for response, survival, or adverse events. CONCLUSION: Single-agent trastuzumab is active and well tolerated as first-line treatment of women with metastatic breast cancer with HER2 3+ overexpression by IHC or gene amplification by FISH.
PMID: 11821453 [PubMed - indexed for MEDLINE]

I reviewed the original paper and patients were excluded from the study if they had less than 6 months to live (estimated, of course), brain or leptomeningeal metastases, more than 30% of their liver taken over by mets, bone mets only, or any significant other medical condition. They had
never been treated with chemo since they had metastatic disease, hence, herceptin was their first line of treatment since developing metastases.

Hope this helps!