Breast cancer spread 'halted'

Thursday January 10 2008

“Scientists discover a way to stop breast cancer spreading”, The Independent ’s headline says. The story underneath says a new discovery could lead to a new form of treatment, “based on preventing tumours from moving from one part of the body to another”.

The newspaper story is based on a study that looked at small molecules of RNA, a chemical that help to control the activity of genes in the cells. The small RNAs appear to control the genes that determine whether the tumour moves away from the site of origin in the breast. This laboratory study may result in the development of useful markers of disease severity but it will be a long wait until drugs based on these genetic fragments become available, if they are developed at all.

Where did the story come from?

Sohail Tavazoie and colleagues from the Memorial Sloan-Kettering Cancer Center, New York conducted the study which was funded by several grants including one from the National Institutes of Health. It was published in the peer-reviewed science journal: Nature .

What kind of scientific study was this?

This was a laboratory study looking at how small pieces of genetic material, called microRNAs, could be involved in enabling cancer cells to spread throughout the body (a process called metastasis).

The researchers used several techniques to identify the microRNAs that appear to slow the spread of cancer cells. The researchers also looked at the cellular mechanisms involved in the suppression of metastasis in mice by these microRNAs and then at the levels of expression of these microRNAs in 20 human breast cancer tumours. The tumours had been surgically removed and stored, and the researchers looked to see whether the levels of microRNAs were related to how well the patients did. 

In order to investigate the effect of microRNAs on human cells, the researchers investigated the effect of restoring the levels of these microRNAs in human cell metastases (the sites where cancers have spread) in mice. Lastly they looked at one specific genetic fragment (miRNA-335) and assessed which genes it might regulate, and how they might play a role in metastasis.

What were the results of the study?

The researchers found that the level of two microRNAs (miR-126 and miR-355) are reduced in human cancer cells that were able to spread (metastasise) in mice, when compared with “parent” non-metastatic cancer cells. If the researchers topped up the levels of these microRNAs, the cells were less able to spread in mice. They also found that levels of these microRNAs were reduced in most primary breast tumours that relapse, and those that were associated with distant spread (metastasis).

What interpretations did the researchers draw from these results?

The researchers suggest that from the multiple parts of this study, there is now sufficient evidence to show that microRNAs are involved in suppressing breast cancer spread.

What does the NHS Knowledge Service make of this study?

This study uncovers some of the mystery as to how some cancers spread quickly and some do not. The identification of a genetic fragment that can slow the growth of breast cancer tumours grown in mice, is good news. The discovery may provide new tools for assessing the aggressiveness of cancers and could also lead to future  improvements in breast cancer treatment.  However promising the technology, much more will need to be known about how we can control these pathways, and studies in humans will be needed.

Sir Muir Gray adds...

Many people are killed not by the cancer at its primary site, but by the secondaries which have spread. Research to halt the spread is as important as research which focuses on the primary tumour.

Analysis by Bazian
Edited by NHS Choices