The first results from the OPTIMA trial were presented at the 2026 American Society of Clinical Oncology (ASCO) Annual Meeting in May.
This trial tested the idea that the results of a specialised laboratory test (Prosigna (PAM50) Assay) of breast tissue could be used to identify people with early ER-positive HER2-negative breast cancer who could safely avoid chemotherapy because there is a low risk of the cancer coming back.
Participants were women and men aged over 40 years, with ER+ HER2- early breast cancer with 0-9 positive axillary nodes and tumour size greater than 30mm if node-negative. These people would normally be offered both chemotherapy and endocrine therapy.
4,429 people participated, including 263 from Australia and New Zealand. 2,215 were assigned to the control arm (given chemo and endocrine therapy regardless of their Prosigna test score) and 2,214 to the test-directed treatment arm (given only endocrine therapy, provided their Prosigna score was < 60, indicating a low risk of recurrence).
The 5-year invasive breast cancer free survival rates (i.e. people who were still alive with no recurrence) were 91.5% for the control group and 90.4% for the test-directed group (i.e. no statistically significant difference), showing that the test-directed treatment regime was not inferior to the standard regime.
68% of the participants (across all groups) had low Prosigna scores (< 60). When only the results from these people were considered, the 5-year invasive breast cancer free survival rates were 94.9% for the control group and 93.7% for the test-directed group (not statistically different). This shows that, for those with low Prosigna scores, there is no benefit derived from receiving chemotherapy as well as endocrine therapy.
The researchers concluded that “The OPTIMA trial demonstrates that women and men with ER positive HER2 negative early breast cancer and ROR (Prosigna) score < 60 tumours can safely avoid chemotherapy.”
You can read more about this trial on our website here, and on the Breast Cancer Trials website here. You can read the scientific abstract of this study here.
18 June 2026
