Chemotherapy is a standard regimen in most cancer treatments. Since it is a very painful process, continuous attempts are made to replace it with something more comfortable for the patient.
Now researchers say that LHRH agonists like the drug Zoladex switch off the ovary and stop the production of a female hormone that encourages some tumours to grow.
An agonist achieves a normal action, often mimicking the action of a naturally occurring substance.
Luteinizing hormone-releasing hormone is a naturally occurring hormone that controls sex hormones in both men and women. Thus, an LHRH agonist serves in a manner similar to LHRH to control the same sex hormones.
Four London centres found that even when used alone, the chemical worked as well as conventional chemotherapy in some cases, the Lancet journal said.
Breast cancer charities say that younger women might benefit the most.
Many types of breast cancer are sensitive to hormones produced naturally by a woman, including the sex hormone oestrogen, and can grow faster if a woman is producing them.
The London researchers, from the Cancer Research UK Centre for Epidemiology, the Wolfson Institute for Preventive Medicine, and Queen Mary's School of Medicine and Dentistry, combined the results of 16 other research projects into LHRH agonists and breast cancer.
When all the different results are added together, the overall findings offer a more reliable indicator as to how well the treatment works.
They found that pre-menopausal women given LHRH agonists did as well as those given standard chemotherapy.
When the two treatments were given together, the women did even better - with cancer 13% less likely to come back.
As expected, LHRH agonists were effective only where a tumour was proven to be sensitive to oestrogen.
The study authors said that the results proved that this was an additional, effective class of drugs in the fight against breast cancer.
Dr Sarah Cant, from Breakthrough Breast Cancer, said that additional research was now needed to see how the drug worked with the most up-to-date types of cancer chemotherapy.
Maria Leadbeater, Clinical Nurse Specialist at Breast Cancer Care, said that the drugs would be particularly useful to younger patients who faced losing their fertility with conventional chemotherapy.