1. ¹Department of Biomedical Sciences and Human Oncology, University of Turin, Torino, Italy
2. ²Unit of Medical Oncology, Institute for Cancer Research and Treatment, Torino, Italy
3. ³Department of Medical Oncology, San Giovanni Hospital, Torino, Italy

Correspondence: Dr G Bussolati, Dipartimento di Scienze Biomediche e Oncologia Umana, Università di Torino, Via Santena 7, 10126 Torino, Italy. E-mail: gianni.bussolati@unito.it

Received 8 September 2004; Revised 1 January 2005; Accepted 8 February 2005.

Abstract

The immunohistochemical determination of HER-2 to identify patients with advanced breast cancer candidates for Trastuzumab treatment proved neither accurate nor fully reliable, possibly because none of the current reagents detects the specific antigenic site target of Trastuzumab. To circumvent this problem, we conjugated the NH₂ groups of Trastuzumab with biotin, and the compound obtained, designated BiotHER, was added directly to tissue sections. Biotin-labelling was revealed with horseradish peroxidase-conjugated streptavidin. Specificity and sensitivity of BiotHER immunostaining with respect to HER-2 amplification were tested on 164 breast carcinoma samples. BiotHER staining was detected on the tumour cell membrane of 12% of all specimens and in 49% specimens with gene amplification, while absent in nonamplified tumours. Predictivity of BiotHER status with respect to the clinical outcome was analysed in 54 patients with HER-2 amplified advanced breast cancer treated with Trastuzumab plus chemotherapy. BiotHER staining, detected in 50% of tumours with HER-2 amplification, was an independent predictor of clinical outcome. In fact, BiotHER positivity was independently associated with increased likelihood of tumour response and reduced risk of tumour progression and death. Biotinylated Trastuzumab can thus be used for immunohistochemical detection of HER-2 overexpression in breast cancer, and has the potential to identify patients likely to benefit from Trastuzumab treatment.