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Published on 8 January 2008

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Fulvestrant “significantly cuts tumour cell growth”

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A high-dose regimen of fulvestrant (Faslodex®) has been shown to reduce tumour cell proliferation, increase oestrogen receptor downregulation and improve likelihood of tumour response, according to a study.

The research, by Dr Irene Kuter of Massachusetts General Hospital, Boston, USA, was presented last month at a breast cancer symposium in San Antonio, USA.

The research showed that a high-dose regimen of the selective oestrogen receptor downregulator significantly (p<0.0001) reduced levels of Ki67 – an important marker of tumour cell growth and a specific indicator of treatment response – compared with the 250mg dose, indicating a greater reduction in tumour cell growth.

The data were from the NEWEST (Neoadjuvant Endocrine Therapy for Women with Estrogen-Sensitive Tumours) Trial.

This randomised phase II study of more than 200 patients compared a high-dose fulvestrant regimen (500mg/month plus 500mg on day 14 of month one) given as 16 weeks’ neoadjuvant therapy for women with ER-positive, locally advanced breast cancer versus the standard 250mg dose.

The primary efficacy endpoint was assessed using levels of Ki67.

Dr Mitch Dowsett, of the Institute of Cancer Research and Royal Marsden NHS Trust London, UK, explained: “Ki67 is an established biomarker of the proliferation of breast cancer cells. The level of Ki67 in the tumour at diagnosis directly relates to a patient’s long-term prognosis and recent studies suggest that it is also a major determinant of treatment benefit.”

In addition to reducing tumour cell proliferation, the 500mg regimen also significantly increased oestrogen receptor downregulation compared to the 250mg dose.

Endocrine treatments such as fulvestrant are designed for patients with hormone receptor positive breast cancer – a type of breast cancer where tumour cells depend on the hormone oestrogen for growth.

In this type of cancer, oestrogen interacts with message-carrying proteins – oestrogen receptors – in the tumour cells.

Due to its mode of action, which is distinct from that of other endocrine treatments, fulvestrant accelerates the breakdown of the oestrogen receptor and disrupts multiple signalling pathways essential for tumour growth.

The NEWEST study data also showed that both regimens were well tolerated and there were no withdrawals due to treatment-related adverse events.

Professor John Robertson, of University of Nottingham City Hospital, UK, added: “The approved 250mg dose of fulvestrant has a well established efficacy profile when used at recurrence or first progression of breast cancer in postmenopausal women with advanced disease and offers clear benefits in terms of controlling the disease and durable responses.

“It will be interesting to see if by using a higher dose in metastatic disease we can deliver even greater benefits for patients.”.

Astra Zeneca

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