Mice lacking a certain enzyme show resistance to the development of breast cancer tumours, a finding that could lead to new treatments for the disease, researchers in Montreal say.

The enzyme is activated by the gene ERBB2, which is found in about 40 per cent of women with breast cancer.

Sofi Julien and biochemistry Prof. Michel Tremblay of the McGill Cancer Centre and their colleagues described the discovery in this week's online issue of the journal Nature Genetics.

"Here for the first time we show that [the gene is] implicated in breast cancer development," said Julien.

The researchers worked with mice that usually develop breast cancer because the animals express the gene too strongly.

The team was able to delay the development of breast tumours using one of two strategies:

• Deleting an enzyme activated by the gene. 
• Giving an inhibitor of the enzyme.

Removing the enzyme, called  protein tyrosine phosphatase 1B or PTP1B, also prevented the cancer from spreading to the lungs.

A medication, Herceptin, already exists that can deactivate the gene and is used to treat women with certain types of breast cancer.

The enzyme inhibitor could be tested in combination with Herceptin in clinical trials within one year, the researchers said.