E2F5 is differentially expressed in the tumors of breast cancer patients treated with trastuzumab.
Trastuzumab (Herceptin) is a monoclonal antibody targeting the extracellular domain of the human epidermal growth factor receptor 2 (HER2) (1) utilized for the treatment of adjuvant and metastatic breast cancer (2) in the United States and worldwide. We mined published microarray and gene expression data (3, 4) to discover in an unbiased manner the most striking transcriptional features of trastuzumab treatment. We identified the transcription factor E2F5 (5) as among the genes most differentially expressed in the primary tumors of patients with breast cancer treated with trastuzumab. The primary tumors of breast cancer patients treated with trastuzumab expressed higher levels of E2F5 messenger RNA than did patients not treated with trastuzumab, and a single administration of trastuzumab was sufficient to result in differential expression of E2F5 in primary tumors of the breast, demonstrating that a transcription factor important for progression of the cell cycle into the S-phase is likely transcriptionally induced by trastuzumab.