A large scale international clinical trial of a new treatment for a form of advanced breast cancer has found the medicine can halt the growth of the illness for more than two years.

Almost two dozen Irish women were among those who took part in the trial of the drug, Palbociclib, which is manufactured by Pfizer in Cork.

The treatment provides a new option to the two thirds of women with a form of metastatic breast cancer that is fuelled by the body's own hormone, oestrogen.

Palbociclib is a combination therapy which is taken alongside an existing hormone suppressant called letrozole.

The new drug is known as a CDK inhibitor that blocks proteins called CDK 4 and 6 in cancer cells.

Blocking these proteins interferes with the ability of the cancer cell to grow, divide, repair and/or communicate with other cells.

The drug has been part of a large international double blind Phase3 clinical trial, involving 666 women in 17 countries, including 22 from Ireland.

The results, published recently in the New England Journal of Medicine, are encouraging.

The PALOMA-2 study found the rate of cancer cell growth was slowed or stopped for a little over two years, compared to 14.5 months for those taking the standard hormone blocker.

"These are very exciting break through findings and have set a new standard for the treatment of this kind of breast cancer", said Dr Janice Walshe, consultant medical oncologist at St Vincent's University Hospital and Tallaght Hospital, who led the trial here in Ireland.

"This finding means that the need for women with this type of cancer to start chemotherapy could be delayed."

Manufactured by Pfizer in Ringaskiddy the drug recently received regulatory approval in Europe and was licensed in the US last year under a fast track programme.

The trial will continue until 2018, to examine the longer term implications for survival rates.

The trial was supported by Cancer Trials Ireland which is funded by the Health Research Board and the Irish Cancer Society.