General Discussion

The Prosigna test, made by the global diagnostics company Veracyte, analyses the activity of 50 genes in tumour tissue. It determines the molecular subtype and provides a score revealing the risk of breast cancer returning in the next decade, helping doctors decide if chemotherapy is worthwhile or not.

The randomised trial involved 4,429 patients aged 40 or above with hormone-positive breast cancer. This is the most common form of breast cancer, accounting for up to 80% of breast cancer cases globally.

Participants were assigned to one of two treatment groups. In the standard treatment group, patients received chemotherapy followed by hormone therapy. In the second group, patients had their tumours analysed with the genomic test.

Those with a high score received chemotherapy and hormone therapy. Those with a low score were treated with hormone therapy alone. Radiotherapy and other treatments were given as usual to both groups.

In the second group, results showed outcomes were extremely similar whether chemotherapy was given or not. Five years after treatment, 95% of those who had chemotherapy and hormone therapy were alive and free from breast cancer recurrence, while 94% of those who skipped chemotherapy were also alive and recurrence-free.

The results suggest that for those with low test scores, chemotherapy offered little or no additional benefit, meaning patients could safely avoid it and its side-effects.