Those who received a high score (above 60) were given chemotherapy and hormone therapy, while those with a low score (less than or equal to 60) were treated with hormone therapy alone.

Of the low-scoring group who did not receive chemotherapy, results showed that outcomes were very similar whether chemotherapy was given or not. Five years after treatment, 94.8 per cent of those who received chemotherapy alongside hormone therapy were alive and free from breast cancer recurrence, and 93.6 per cent of those treated with hormone therapy alone were also alive and recurrence-free.

Doctors said the results show that people aged 40 or older with hormone‑sensitive breast cancer and a low Prosigna score can safely avoid chemotherapy.