Hormones released during pregnancy raise levels of a protein that blocks the growth of breast cancer, say scientists.

Although the research is at an early stage, they believe it could lead to new treatments.

It is well known that pregnancy hormones such as oestrogen, progesterone and human chorionic gonado-tropin reduce the risk of breast cancer.

However, the reason is not clearly understood.

Part of the answer may be that the hormones trigger the production of a protective protein, a new study suggests.

Alpha-fetoprotein (AFP) is normally generated in the liver and the foetal yolk sac, which supplies an unborn baby with its first nutrients.

US scientists conducted experiments with rats at high risk of mammary cancer. The animals were treated with oestrogen alone, oestrogen plus progesterone, or human chorionic gonadotropin.

In a large proportion of the rats, the hormones prevented or delayed the development of mammary cancers, and each treatment also raised blood levels of AFP.

Defence

When laboratory cultures of breast cancer cells were exposed to AFP, their growth was blocked. The scientists believe this suggests it is the protein that is responsible for the protective effect of pregnancy hormones.

Lead researcher Dr Herbert Jacobson, from Albany Medical College in New York, said: "Hormones in pregnancy, such as oestrogen, all induce AFP, which directly inhibits the growth of breast cancer.

"The body has a natural defence system against breast cancer.

"AFP needs to be safely harnessed and developed into a drug that can be used to protect women from breast cancer."

The findings are published today in the journal Cancer Prevention Research.

Professor Powel Brown said it was too soon to think about patients benefiting

He pointed out there was no direct evidence of AFP having an anti-cancer effect, and mammary tumour growth was not blocked in all the rats.

"This study is promising and suggests that additional animal studies need to be done before translation to humans," said Prof Brown, from the University of Texas.

"We may want to further test AFP for its cancer prevention activity."

hnews@herald.ie

- John von Radowitz