Oncotype DX Recurrence Score in Very Small Tumors: Does Recurrence Score Influence Clinical Outcome?

Tumor size is an established and independent risk factor for locoregional recurrence (LRR) and distant metastasis. More recently, the recurrence score (RS) calculated from a 21-gene expression assay (Oncotype DX, Exact Sciences) has been shown to correlate with LRR and distant metastasis. This study sought to evaluate the impact of RS on recurrence risks for small tumors (≤1 cm) with RS ≥26 to similar-sized tumors with RS <26.

Between 2008 and 2020, 231 patients with breast cancers measuring ≤1 cm and high RS of ≥26 were retrospectively identified. These were compared with a control cohort of 1747 breast cancers that were ≤1 cm with RS <26 over the same time interval. Rates of LRR and invasive recurrence (IR)-free interval were estimated using the Kaplan-Meier method, and multivariable Cox regression was conducted.

Patients with RS ≥26 had significantly worse time to LRR (P < .001) and IR than patients with RS <26 (P < .001). The LRR-free probabilities for RS ≥26 and RS<26 patients are 94% versus 99% at 5 years and 88% versus 96% at 10 years. Similarly, the IR-free probabilities were 94% versus 99% at 5 years and 87% versus 95% at 10 years. In multivariable analyses, RS was independently associated with LRR and IR.

Our findings suggest that patients with small tumors and high RS are at a higher risk for LRR than patients with ≤1 cm breast cancers with low RS, despite the best available standard-of-care treatment. These findings may have important implications for the tailoring of locoregional treatment strategies because they relate to omission of radiation therapy and selection of radiation therapy modality.