For a 58-year-old woman with a 3.2 cm, grade 2, estrogen‑receptor‑positive, progesterone‑receptor‑positive, HER2‑negative invasive ductal carcinoma, two positive axillary lymph nodes, high clinical risk, and a low Prosigna (PAM50 Risk of Recurrence) score, what is the most appropriate adjuvant treatment step according to the OPTIMA trial presented at ASCO 2026?

Omit Chemotherapy and Treat with Endocrine Therapy Alone

For this patient with high clinical risk but a low Prosigna (PAM50 ROR) score, the most appropriate next step is to omit chemotherapy and proceed with endocrine therapy alone (Answer B), based on the OPTIMA trial paradigm that genomic risk supersedes clinical risk in treatment decision-making.

Evidence-Based Rationale

The OPTIMA trial, presented at ASCO 2026 (referenced in the clinical scenario), specifically addresses this exact clinical dilemma: patients who are clinically high-risk (like this patient with 3.2 cm tumor, grade 2, and 2 positive nodes) but have low genomic risk by PAM50 ROR score. The trial's fundamental premise is that genomic risk assessment can identify patients who can safely omit chemotherapy despite adverse clinical features.

Supporting Validation Data

The Prosigna assay has robust validation in node-positive disease:

• In a comprehensive Danish cohort 1, 26% of node-positive patients were classified as low ROR, with only 3.5% experiencing distant recurrence at 10 years with endocrine therapy alone (95% CI: 1.9%-6.1%). This demonstrates that low ROR scores reliably identify a subset of node-positive patients with excellent outcomes without chemotherapy.

• The MINDACT trial 2 established the precedent that genomic low-risk can override clinical high-risk: among patients with high clinical risk/low genomic risk (21% had 1-3 positive nodes), the 5-year distant metastasis-free survival was 94.7% without chemotherapy.

Why Other Options Are Incorrect

Option A (chemotherapy per standard protocol) contradicts the entire purpose of genomic testing and ignores validated evidence that low ROR identifies patients who derive minimal-to-no benefit from chemotherapy.

Option C (repeat with different assay) is unnecessary and delays treatment. While Oncotype DX is validated in node-positive disease 2, there is no evidence that discordant results between assays should prompt retesting. The Prosigna assay is specifically validated for this clinical scenario 1.

Option D (clinical trial referral) is incorrect because genomic testing is validated in node-positive disease. Both MINDACT (70-gene assay) and multiple Prosigna validation studies 1 included node-positive patients. Current NCCN guidelines 2 explicitly recommend gene expression assays for node-positive disease to guide chemotherapy decisions.

Option E (CDK4/6 inhibitor without chemotherapy) represents a potential alternative, but this is not the standard approach based on OPTIMA trial design. The MonarchE criteria 2 for abemaciclib require either ≥4 positive nodes OR 1-3 positive nodes with additional high-risk features (grade 3 or tumor ≥5 cm). This patient has grade 2 disease with 3.2 cm tumor, which doesn't clearly meet high-risk criteria. More importantly, the OPTIMA trial specifically evaluates endocrine therapy alone versus chemotherapy plus endocrine therapy in genomically low-risk patients—CDK4/6 inhibitors are not part of this comparison.

Clinical Implementation Algorithm

1. Confirm low ROR score is documented and HER2-negative status verified
2. Proceed with endocrine therapy alone:
   • For this 58-year-old woman, determine menopausal status 2
   • If postmenopausal: aromatase inhibitor (preferred) or tamoxifen
   • If premenopausal/perimenopausal: tamoxifen + ovarian suppression or aromatase inhibitor + ovarian suppression
3. Consider adjuvant bisphosphonate for 3-5 years given node-positive status 2
4. Do not add chemotherapy based on low genomic risk

Critical Caveats

• The absolute benefit of chemotherapy in low ROR, node-positive disease is minimal (approximately 1-2% reduction in recurrence risk based on 1)
• This recommendation assumes the Prosigna test was performed correctly on adequate tissue
• Patient counseling should acknowledge the 3.5% 10-year distant recurrence risk with endocrine therapy alone 1, which most patients find acceptable given chemotherapy toxicity
• The OPTIMA trial design validates that genomic risk assessment should guide treatment decisions over clinical risk factors alone in ER+/HER2- disease

The paradigm shift established by trials like OPTIMA is that multigene assays identify tumor biology that supersedes traditional clinical and pathological risk factors in predicting chemotherapy benefit 2, 1.