A compound that appears to target the master cells which help breast cancers grow and spread has been discovered by US scientists.

美国科学家发现了以主要细胞为对象帮助癌细胞生长并扩散的混合物。

Some 16,000 chemicals were tested by researchers

In tests in mice, salinomycin（盐霉素） killed breast cancer stem cells（干细胞） far more effectively than some existing drugs, and slowed tumour¹ growth.

The drug, a farm antibiotic²（抗生素）, has yet to be tested in humans, the journal Cell reports.

But UK experts warned a human version could be some years away.

The reasons why, even following powerful chemotherapy（化学疗法）, some cancers can grow back, are not fully³ understood.

Many scientists believe a key role lies with stem cells, which can be resistant⁴ to（对……有抵抗力的） conventional（普通的，常见的） chemotherapy, remaining to 'seed' new tumours⁵ and drive their growth.

The drug's potential was identified by researchers at the Massachusetts Institute of Technology, who tested 16,000 existing chemical compounds against breast cancer stem cells in the laboratory.

Those which performed the best were then tried in mice, and compared to existing drugs such as paclitaxel（紫杉酚）.

Salinomycin appeared to be 100 times better at killing⁶ the cells in a test tube, and treated cells were much less likely to start new tumours when injected into mice.

When given to mice with tumours, the growth of the cancer slowed.

However, the researchers stressed that it was too early to know if similar successes could be achieved in human cancer patients.

"Many therapies kill the bulk of a tumour only to（不料竟会） see it regrow," said Professor Eric Lander, from MIT."This raises the prospect⁷ of new kinds of anti-cancer therapies."

'Very early research'

Dr John Stingl, group leader in mammary stem cell biology at Cancer Research UK's Cambridge Research Institute, said: "This is one of the biggest advances we have seen this year in this area of research. These scientists have demonstrated that it's possible to selectively target the rare cancer stem cells that drive tumour growth.

"This research also introduces a completely new way of identifying cancer drugs. The challenge for the future is to bring this class of drugs to the clinic and to identify the patients that are likely to respond to them."

Dr Alexis Willett, head of policy at Breakthrough Breast Cancer, added: "There is evidence that stem cells may enable breast cancers to form and grow.

"This research provides a clue as how to identify these cells and how they might be targeted and destroyed. "It's important to remember that this is very early research and it will be some time before it is clear whether this leads to an effective breast cancer treatment."