Abstract PO2-01-10: 21-Gene Recurrence Score Index (ONCOTYPE DX) as a predictive biomarker for neoadjuvant chemotherapy response and outcome in patients with HR+HER2- breast cancer

Abstract Background: Hormone receptor positive (HR+), HER2- early stage breast cancer (EBC) has shown lower response to neoadjuvant chemotherapy (NCT) compared with other clinicopathologic subtypes. ONCOTYPE DX may help inform systemic treatment decisions for EBC and predicting likelihood of pathological complete response (pCR) or chemosensitivity. We analyze the pathologic response according ONCOTYPE RS and their prognostic value. Methods: We included a serie of 139 consecutive patients with high clinical risk factor with criteria to received NCT than have performed an ONCOTYPE DX test previous to start NCT. The median age was 51 years with 65 patients (47%) less than 50 years. Median initial tumoral size was 25 mm (9-97), T1: 35%, T2: 51% and T3: 14%. 70 patients (50%) have initial axillary node involvement. Median ONCOTYPE DX score was 29 (12 – 76) , RS 25 in 36% and RS 30 in 54%. Complete pathologic response (pCR) was found in 35 patients (25%), and by RCB was: RCB:0 23%, RCB-1 18%, RCB-2 24% and RCB-3 34%. Results: pCR score was correlated with ONCOTYPE DX (pearson : p:0,001) , patients with ONCOTYPE RS score superior to 30 has a total of 37% of pCR in contrast to a 14% in patients with ONCOTYPE RS score less than 30. Median follow-up was 32 months (5 -100). The rate of recurrence was similar independently the ONCOTYPE RS score (12% 30 ; 15% 30) , but patients with ONCOTYPE RS 30 with achieve pCR had better prognostic compared to patients that not achieve pCR (0% vs 14%). Patients with ONCOTYPE RS 30 tumors that had a pCR the recurrence rate was 8% compared to 20% in patients with non pCR. Conclusions: These data suggest ONCOTYPE DX predicts pCR in HR+HER2- BC patients, especially in patients with a RS superior to 30 with an high rate of pCR of 37%. Patients with ONCOTYPE DX less than 30 that achieved pCR had the better outcomes and patients with ONCOTYPE DX superior to 30 that not achieved pCR had the worst outcomes with a total of 20% of recurrence. ONCOTYPE DX predicts the possibility of achieve a pCR and patients with a high ONCOTYPE DX RS score with residual disease have a high recurrence despite receiving treatment with chemotherapy, which requires a better adjuvant treatment, possibly with CDK 4/6 cyclin inhibitors. Citation Format: Ariadna Gasol Cudós, Serafin Morales Murillo, Noemí Tuset Der-Abrain, Felip Vilardell Villellas, Laura Arbones Cid, Jordi Melé Olivé, Carles Canosa Morales. 21-Gene Recurrence Score Index (ONCOTYPE DX) as a predictive biomarker for neoadjuvant chemotherapy response and outcome in patients with HR+HER2- breast cancer abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-01-10.