Prof Mitch Dowsett
told the opening press conference at the European Breast Cancer Conference (EBCC-9) that his
research had shown that women who had tumours that were negative for the human epidermal growth factor protein (HER2-) but which were very sensitive to the oestrogen hormone, had more than double the risk of their cancer recurring between five and ten years after surgery and five years of adjuvant hormone therapy.
"Our data suggest that these patients, who are those that appear to benefit most from the current standard five years of endocrine treatment, may also benefit from adjuvant hormone treatment that extends beyond that five years," said Prof Dowsett, who is Professor of Biochemical Endocrinology at The Institute of Cancer Research, London, and Head of Biochemistry at The Royal Marsden NHS Foundation Trust, London.
colleagues at The Royal Marsden
, the ICR, and Queen Mary University of London (UK) used data from the OncotypeDx® 21-gene Recurrence Score that are not usually available from this test in order to analyse the genetic make-up and to predict the likelihood of cancer recurring within ten years in these women.
"The OncotypeDx result is reported as a single score but it is made up of 16 informative genes and five control or "housekeeper" genes that we have studied in detail.
Some of the 16 are considered as groups rather than individual genes, and one of these is the E-module, which consists of four genes that are related to oestrogen signalling, including the oestrogen receptor itself," he
"When we looked at the women with HER2- breast cancer and defined them according to their E-module score, which indicated how sensitive to oestrogen their tumours were, we found that there was a striking difference," said Prof Dowsett
"Among women with tumours most sensitive to oestrogen, with a high E-module score, the recurrence rate more than doubled from 5.7% in the first five years to 13.6% in the subsequent five years.
However, if they had a low E-module score, there was little difference in recurrence rates between the first five years and the next five years: 10.3% versus 12.3%."
The researchers say that their results show that, despite similar overall recurrence rates for patients with ER+ tumours between the first five years and the next five to ten years, there were important differences between groups of tumours with different genetic expression profiles.
"Importantly, HER2- tumours that are very sensitive to oestrogen are usually considered to be relatively low risk, yet these were the tumours that showed an increase in recurrence after five years, which coincided with the cessation of adjuvant hormonal therapy," said Prof Dowsett
"This should be done by testing the tumours of patients that are participating in ongoing trials of extended versus no extended adjuvant therapy," said Prof Dowsett