Thousands of breast cancer patients currently prescribed chemotherapy can safely avoid the “gruelling” treatment, according to a new trial hailed as the biggest advance in cancer practice for 20 years.

A long-term study of women with the most common form of the disease found less than a third should be put on the drugs, rather than the 50 per cent traditional figure.

The trial found that for a significant proportion of the patients diagnosed at an early stage, their survival chances were just as good if they took only oral hormone medication, which comes with far fewer risks and side-effects.

The results have been welcomed as “fantastic news” by cancer charities, while leading oncologists said they should “transform care immediately”.