The trial with Palbociclib will be run in six hospitals
Fifty patients in Cork, Waterford and Dublin are to get access to drug not yet approved in Ireland for early stage breast cancer.
The Irish arm of a global cancer trial, which will involve 4,600 patients in 500 hospitals around the world, has been opened by Cancer Trials Ireland.
It will investigate the new drug, Palbociclib.
Organisers say they want to see of the drug decreases the chance of cancer recurring in women and men with early stage HR positive/HER2 negative breast cancer, when it is given in combination with the current standard anti-hormone therapy.
The trial will be run in six hospitals: Cork University Hospital, University Hospital Waterford, and in Dublin, Mater Hospital, Beaumont Hospital, St James's Hospital and St Vincent's University Hospital.
Patients interested in taking part in the trial should contact their medical oncologist.
Dr Patrick Morris, consultant medical oncologist at Beaumont Hospital Dublin, is also co-chair of the breast group of Cancer Trials Ireland.
"No new drugs have been developed for early stage breast cancer for a number of years.
"In the last decade our research has focused on different durations and combinations of available hormone therapy.
"Palbociclib was used in a trial among patients with advanced breast cancer, which is when cancer has spread from the original tumour, and the recently published results show that it reduced the rate of cancer growth by up to 42% when compared to standard hormone therapy alone.
"Given these impressive results for advanced breast cancer, we are tremendously excited about investigating its potential in early stage breast cancer."
Dr Morris added: "While many patients with early stage breast cancer respond very well to standard anti-hormone therapy and are cured, there remains a risk of recurrence, particularly for those patients with involved lymph nodes.
"So we need to improve the effectiveness of current treatments for these patients and find ways to stop or delay recurrence of their cancer."
The primary treatment for patients with early stage breast cancer can involve a combination of surgery, chemotherapy, hormone therapy and/or radiotherapy.
The trial will test whether Palbociclib, used in combination with the standard post-operative anti-hormone therapy, will produce better results than the current standard anti-hormone therapy alone.