Herceptin Research Today is a free monthly online journal that collates and summarizes the latest research about Herceptin, including details on side-effects, breast cancer, treatment, therapy.

The combination of letrozole and trastuzumab as first or second-line biological therapy produces durable responses in a subset of HER2 positive and ER positive advanced breast cancers.

Marcom PK, Isaacs C, Harris L, Wong ZW, Kommarreddy A, Novielli N, Mann G, Tao Y, Ellis MJ

Duke Comprehensive Cancer Center, Duke University, Durham, NC, USA.

BACKGROUND: Estrogen receptor (ER) and/or progesterone receptor expression occurs in approximately 50% HER2 positive (HER2+) breast cancers and cross-talk between the estrogen and HER2 pathways promotes endocrine therapy resistance. The efficacy of the aromatase inhibitor letrozole in combination with trastuzumab was therefore tested in a Phase 2 study. METHODS: Patients with ER+ and/or PgR+ and HER2+ (IHC 2+ or 3+ or FISH+) advanced breast cancer were treated with trastuzumab plus letrozole until disease progression or unacceptable toxicity. RESULTS: Thirty-three patients were enrolled, of which thirty one were considered evaluable. The majority of patients (82%) had received tamoxifen and 82% had HER2 FISH+ and/or IHC 3+ tumors. Eight patients responded (1 CR and 7 PR) for an overall response rate (ORR) of 26% and a clinical benefit rate (CBR) of 52%. The median time to progression (TTP) was 5.8 months and the median duration of response (DOR) was 20.6+ months. Excluding IHC 2+, FISH- tumors, the OR was 24%, CBR 44%, TTP 5.5 months and DOR 17+ months. The combination was well tolerated with only two toxicity events requiring termination of study medication. CONCLUSIONS: Combined trastuzumab and letrozole treatment for patients with HER2+ and ER+ advanced breast cancer produced durable responses consistently lasting at least 1 year in one quarter of the patients. While these data are promising for a subgroup, for half the patients, trastuzumab plus letrozole was inactive. This finding demonstrates ER+ HER2+ advanced disease is heterogeneous and additional agents will be required for optimal management based on targeted therapeutics alone.

Published 9 August 2006 in Breast Cancer Res Treat.
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