Could Genomic Testing Help Some Breast Cancer Patients Avoid Chemotherapy?
Guest Contributor
For many people diagnosed with estrogen receptor–positive, HER2-negative early breast cancer, one of the biggest fears is not just the disease itself but the possibility of needing chemotherapy. The side effects can be harsh, long lasting, and life altering. New data from the phase III OPTIMA trial suggest that a substantial proportion of these patients, even those considered clinically high risk, may safely avoid chemotherapy when treatment is guided by tumor gene expression testing such as the Prosigna assay.
The OPTIMA trial focused on a familiar and increasingly important question in early breast cancer: who truly needs chemotherapy, and who can do just as well with endocrine therapy alone? Tumor gene expression assays are already widely used to guide chemotherapy decisions for postmenopausal patients with limited lymph node involvement. What has been less clear is whether these tools can be trusted in younger, premenopausal patients, or in those with more extensive lymph node involvement. OPTIMA was designed to test exactly that.
Led by Robert Stein of University College London Hospitals, this international randomized noninferiority study enrolled 4,429 individuals aged 40 years or older with estrogen receptor–positive, HER2-negative early breast cancer. All had high clinical risk features. Patients could have up to nine positive lymph nodes, and those with no involved nodes needed tumors larger than 3 cm to be eligible. These characteristics placed them among the higher risk end of the early breast cancer spectrum.
Participants were randomly assigned to one of two strategies. In the control arm, everyone received standard chemoendocrine therapy. In the test-directed arm, treatment decisions were guided by the risk-of-recurrence (ROR) score from the Prosigna assay, a PAM50-based gene expression test. Those with a high ROR score above 60 received chemotherapy plus endocrine therapy, mirroring the control arm. Those with an ROR score of 60 or lower received endocrine therapy alone without chemotherapy. Premenopausal women aged 40 or older who did not develop chemotherapy-induced ovarian insufficiency also received ovarian function suppression as part of their endocrine therapy regimen.
The central hypothesis of OPTIMA was that for tumors with a low genomic risk, the number of involved lymph nodes does not meaningfully affect the benefit from chemotherapy. In other words, if the tumor biology is favorable according to Prosigna, then chemotherapy may add little even in patients with several positive lymph nodes. This question has been an important gap in evidence, because prior genomic trials such as TAILORx, MINDACT, and RxPONDER largely focused on patients with zero to three involved nodes or had limited data on those with more extensive nodal disease.
After a median follow-up of 4 years, OPTIMA met its primary goal of showing noninferiority of the test-directed approach compared with standard chemoendocrine therapy. In the full per-protocol population, the 5-year invasive breast cancer–free survival rate was 91.8% in the control arm and 90.3% in the test-directed arm. The hazard ratio was 1.03, and the noninferiority test was statistically significant. These results suggest that allowing Prosigna to guide chemotherapy decisions did not compromise overall invasive breast cancer control at 5 years.
The data were particularly striking among patients whose tumors had low ROR scores. In this group, 5-year invasive breast cancer–free survival was 94.8% for those given routine chemoendocrine therapy and 93.6% for those who typically received endocrine therapy alone. The hazard ratio was 1.06 with strong statistical support for noninferiority. Stein summarized the practical implication succinctly. According to his presentation, Prosigna identifies roughly two-thirds of this high clinical risk population as unlikely to derive meaningful benefit from chemotherapy. At most, he said, chemotherapy would prevent about two recurrences for every 100 such patients treated.
Subgroup analyses showed that this pattern held across different clinical settings. Among patients with low ROR scores, premenopausal participants had 5-year invasive breast cancer–free survival of 95.5% with standard chemoendocrine therapy and 94.2% with the test-directed approach. Postmenopausal patients showed similarly close outcomes, 94.5% versus 93.2%. For those with one to three positive lymph nodes, survival rates were 95.2% with standard treatment and 93.6% with test-directed care. Even among patients with four to nine positive nodes, considered a particularly high-risk group, invasive breast cancer–free survival was 93.1% in the control arm and 91.5% in the test-directed arm.
Distant recurrence–free survival, an outcome that many clinicians and patients watch closely, also looked reassuring. In the full per-protocol population, the 5-year rate was 94.1% with chemoendocrine therapy and 93.3% with the test-directed strategy. For patients with low ROR scores, distant recurrence–free survival reached 97.0% in the control arm and 96.0% in the test-directed arm. These small numerical differences suggest that endocrine therapy plus ovarian function suppression, when paired with a favorable multigene test result, can be a robust alternative to adding chemotherapy.
Jame Abraham of Cleveland Clinic, who has closely followed the evolution of genomic assays in breast cancer, described the updated OPTIMA results as an important addition to the growing body of prospective evidence. Trials such as MINDACT, RxPONDER, and TAILORx together with OPTIMA now encompass about 18,000 patients. Across these studies, Abraham noted a consistent theme. In the presence of a favorable multigene expression profile, ovarian suppression combined with endocrine therapy is not inferior to endocrine therapy plus chemotherapy, even when traditional clinical features suggest higher risk.
There are important nuances, and Abraham highlighted several. One relates to follow-up time. Estrogen receptor–positive breast cancer is known for late recurrences that can appear many years after initial diagnosis. With only 4 years of median follow-up, some clinicians may feel cautious about drawing definitive conclusions. Longer-term data from OPTIMA will be especially valuable to see whether these early patterns persist at 10 years and beyond. Stein noted in response that meta-analyses from the Early Breast Cancer Trialists’ Collaborative Group show most of the impact of chemotherapy on recurrence occurs within the first 5 years and that time-dependent changes have not been evident in related trials so far, yet ongoing observation remains essential.
Another caveat involves the specific genomic test. The Prosigna assay uses a 50-gene PAM50-based signature to calculate its ROR score. In many current guidelines, including those from the National Comprehensive Cancer Network, Oncotype DX is the more familiar and preferred assay for early-stage estrogen receptor–positive, HER2-negative disease. How Prosigna’s ROR score compares directly with the Oncotype DX recurrence score remains an open question. Clinicians who routinely use Oncotype DX may need additional translational work before they feel comfortable integrating Prosigna into everyday decisions, particularly for patients with multiple positive nodes.
Even with these cautions, the message that emerges from OPTIMA is hopeful. For a large proportion of patients with estrogen receptor–positive, HER2-negative early breast cancer who are clinically high risk but genomically low risk, chemotherapy may not be necessary to achieve excellent outcomes. This includes not only postmenopausal individuals but also premenopausal women aged 40 and older who receive effective ovarian suppression. For patients facing treatment decisions, trials like OPTIMA support more personalized, biology-driven care rather than a one-size-fits-all approach.
Abraham emphasized that treatment decisions should remain grounded in shared decision-making. Multigene assays can provide powerful information about likely benefit from chemotherapy, but individual preferences, tolerance for risk, and concerns about side effects all play an important role. With data from OPTIMA now joining previous trials, clinicians and patients have more evidence to inform thoughtful conversations about when chemotherapy is truly needed and when endocrine therapy with ovarian suppression may be enough.