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Breast cancer tumours change as disease progresses

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Swedish researchers have made a new discovery that throws into question how doctors decide on treatments for breast cancer patients.

Normally the decision about the most effective treatment for the patient is made based on one biopsy of the primary tumour; however, this new study shows that in fact breast cancer tumours change their hormonal status throughout the course of the disease. The researchers believe that armed with more accurate biopsy results after a relapse, doctors can advise on more targeted individual treatment.

By carrying out oestrogen (ER) and progesterone (PR) receptor status tests, scientists can see whether one or both of these hormones is helping to grow the cancer. Cancer that is hormone positive can be treated by hormone-suppressing drugs, whereas hormone negative cancers may respond to other types of treatment. Hormone negative patients are normally tested for human epidermal growth factor receptor 2 (HER2). If this test is positive, treatment such as Herceptin will usually be given.

Therefore if these factors change throughout the disease lifetime, treatment given at the beginning might not be effective further down the line.

'Our study demonstrates tumour instability in clinically used markers throughout tumour progression. We saw, for example, that one in three breast cancer patients alter ER or PR hormone receptor status, and 15% of patients change HER2 status during the course of disease,' comments lead researcher Linda Lindström, from the Karolinska Institutet in Sweden.

Linda Lindström is presenting the findings from the study, the first major study to look at changes in tumours in multiple relapses in breast cancer patients, at the 2011 European Multidisciplinary Cancer Congress in Stockholm, Sweden, which began on 23 September and runs until 27 September and is organised by the The European CanCer Organisation (ECCO).

The study is based on an analysis of breast cancer patients in the Stockholm healthcare region who had a recurrence of the disease between 1 January 1997 and 31 December 2007.

The findings show that 33.6% of patients had changes in tumour status between the different sites of relapse (local, loco-regional and metastases) whereas 36.1% of the patients were stable ER positive, and 30.3% were stable ER negative. Sixteen percent of patients changed from ER positive to negative during the course of their disease, 12.6% changed from negative to positive, and 5% altered back and forth throughout tumour progression.

In the PR positive group, 30.2% of patients altered their hormone receptor status, with the majority changing from positive to negative.

'Until now we thought that these predictive markers remained stable during the course of the cancer. But it is now apparent that these breast tumours markers, which are used to decide the best treatment for the patient, change as the tumour progresses and this significantly affects the way patients respond to particular therapies. This has important implications for the future management of the disease,' says Dr Lindström.

With the conclusion that taking regular biopsies in patients who relapse is essential to ensure they are getting the most appropriate treatment, the team now hope that their findings will trigger research into other types of cancer as they have a hunch that what they have seen in this study could also apply across the board.

'We believe that tumour instability may be due to many different factors, for instance the choice of therapy and other host (patient) characteristics, and that some inherent tumour behaviour may well be shared by different tumour types. This is a promising area of research with important implications for patient management,' says Dr Lindström.

The European CanCer Organisation represents professionals in oncology and proactively engages with policymakers to ensure that oncology matters stay at the top of European governments' agendas