Broccoli and breast cancer

Behind the Headlines

Wednesday May 5 2010

This study does not prove that eating broccoli will stop cancer

“Broccoli could stop breast cancer spreading,” according to the Daily Mail. The newspaper says that sulforaphane, a chemical found in the “green superfood”, targets the cells that fuel the growth of tumours.

This valuable laboratory research has found that sulforaphane, appears to have anti-cancer properties. In human breast cancer cells in a laboratory, and in mice injected with cancer cells, treating cells with sulforaphane was found to prevent the growth of breast cancer stem cells and thus halt the tumour’s progression.

These findings will undoubtedly lead to further testing of the anti-cancer properties of sulphoraphane and its potential to target cancer stem cells. Current chemotherapy and radiotherapy regimes are reportedly incapable of doing this. However, this research is in the very early stages, and there are no immediate implications for breast cancer treatment or prevention. It cannot be assumed that eating broccoli has the same effect as applying sulforaphane directly to cancer cells in a laboratory. A lot more research is needed to ascertain this.

 

Where did the story come from?

Yanyan Li and colleagues from the University of Michigan and Ohio State University carried out this research. The study was funded by the University of Michigan Cancer Center Research Grant, and the University of Michigan Cancer Center Core Grant. The study was published in the peer-reviewed medical journal Clinical Cancer Research.

This research has generally been well represented by the Daily Mail. However, people should not be confused into thinking that these laboratory findings mean that eating broccoli is likely to stop cancer in its tracks.

 

What kind of research was this?

This was a laboratory study, which has aimed to examine how cancer stem cells in breast cancer are affected by sulforaphane, a natural chemical found in broccoli and broccoli sprouts. The potential for the compounds in broccoli and other cruciferous vegetables to prevent cancer has been frequently studied. Sulforaphane is believed to ‘block’ the conversion of pro-carcinogen chemicals into carcinogens, enhance their breakdown in the body, and also ‘suppress’ the growth of cancerous cells. Several cancers, including breast cancer, are believed to be initiated by the growth of a group of cancer stem cells that continuously renew and change into different cell types. These cancer stem cells are believed to be involved in cancer relapse and resistance to treatment.

This particular research involved applying sulforaphane to breast cancer cells in a laboratory, and looking at the chemical’s effect on cell growth. This is valuable research, but it must be interpreted in this context. Applying the compound directly to the cells outside of the body and injecting the compound into mouse models cannot be assumed to be comparable to eating broccoli. This early, speculative research has no immediate implications for cancer treatment or prevention.

 

What did the research involve?

The researchers obtained and cultured two different breast cancer cell lines called MCF7 and SUM159, of which the latter is negative for the presence of oestrogen and progesterone receptors. They treated both cell lines with increasing concentrations of sulforaphane. They used various different laboratory methods to assess the number of living cancer cells found after 48 hours of incubation with protein and sulforaphane, and looked at the activity of an enzyme called aldehyde dehydrogenase, which is believed to ‘enrich’ cancer stem cells.

They also carried out a process called a ‘mammosphere formation assay’, which promotes the growth of breast cancer stem cells. They looked at how this was affected by seven days incubation with sulforaphane.

In a separate part of the experiment, the researchers then injected SUM159 cancer cells into the mammary glands of immuno-deficient female mice. After two weeks of tumour growth, they divided the mice into two groups. One group received daily injections of a sulforaphane solution over a further period of two weeks, and another group was injected with a ‘control’ salt solution.

After this time, they extracted the tumours from the mice and examined how cancer stem cells were affected. They then re-implanted living cancer cells extracted from the sulforaphane-treated and control-treated tumours into a secondary group of mice to monitor how the tumours grew.

 

What were the basic results?

The researchers found that incubating breast cancer cell lines with sulforaphane reduced the size and number of breast cancer stem cells. It also reduced the number of cells that were positive for the aldehyde dehydrogenase enzyme thought to enrich cancer stem cells. In the mice, daily injection with sulforaphane for two weeks reduced the number of aldehyde dehydrogenase-positive cells. It also eliminated breast cancer stem cells. When these sulforaphane-treated tumour cells were then re-implanted into the second group of mice, tumour growth was prevented.

 

How did the researchers interpret the results?

The researchers concluded that sulforaphane inhibits breast cancer stem cells and limits their rate of self-renewal. They say that their findings "support the use of sulforaphane for the chemoprevention of breast cancer stem cells", and they warrant further clinical evaluation.

 

Conclusion

This valuable laboratory research has found that sulforaphane, a natural compound found in broccoli and broccoli sprouts, does appear to have some anti-cancer properties. In human breast cancer cells in the laboratory, and in mice that had been injected with these cancer cells, directly treating the cells with sulforaphane was found to prevent the growth of breast cancer stem cells and thereby halt progression of the tumour.

These findings will undoubtedly lead to further research into the possible uses of this compound in preventing and treating cancer by targeting this stem cell population. This is an action that current chemotherapy and radiotherapy regimes are reportedly incapable of doing, and which could play a role in non-responsive or relapsing of tumours.

However, this research is in the very early stages, and there are no immediate implications for breast cancer treatment or prevention. Most importantly, it cannot be assumed that eating broccoli is comparable to applying the sulforaphane compound directly to cancer cells under controlled conditions.

Analysis by Bazian

Edited by NHS Choices

Links to the headlines

Broccoli could stop breast cancer spreading by targeting stem cells. Daily Mail, May 5 2010

Links to the science

Li Y, Zhang T, Korkaya H, et al. Sulforaphane, a dietary component of broccoli/broccoli sprouts, inhibits breast cancer stem cells. Clinical Cancer Research 2010; Published online first, April 13

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