Factors associated with benefit of adjuvant chemotherapy in patients with T1b/T1c HR-positive/HER2-negative breast cancer and high multigene recurrence score.
Authors: Maria Herran, Saad Sabbagh, Ali Hijazi, Mohamed Mohanna, Kaylee Sarna, Barbara Dominguez, Zeina A. Nahleh
Journal: Journal of Clinical Oncology (2024)

e12540 Background: Patients diagnosed with early-stage HR-positive/HER2-negative Breast Cancer (BC) and high Oncotype DX Recurrence Score (RS ≥26) are offered adjuvant chemotherapy and endocrine therapy compared (CET) to endocrine therapy alone (ET). We sought to investigate if additional clinical factors that could further determine benefit from chemotherapy in patients with T1b/T1c and N0 tumors with high Oncotype DX to help deescalate treatment by avoiding chemotherapy induced toxicity. Methods: The purpose of this study is to determine the clinical factors associated with a survival difference from CET compared to ET alone in T1b/T1c and N0 BC. We analyzed the record of patients diagnosed with T1b/T1cN0M0 HR-positive/HER2-negativeBC and RS ≥26 between 2006 and 2020 from the National Cancer Database. Patients were separated into two groups based on their treatment: CET or ET and the following characteristics were assessed: age, grade, histology, and RS (26-30, 31-40, 41-100) to determine overall survival differences among the two groups. Chi-square was performed to evaluate the association between baseline categorical characteristic variable and chemotherapy treatment. Survival analysis of treatment modalities using Kaplan Meier curves and univariate Cox regression. Multivariate Cox regression with backwards elimination was performed for subgroup analyses. Results: A total of N=19,373 eligible patients were identified, n=14,422 (74.4%) received CET and the rest ET alone. The mean age at diagnosis was 59.6 years (SD=10.3); 86.6% presented with invasive ductal carcinoma and 83.3% had a Charlson-Deyo Comorbidity Score of 0. In the overall group, patients who received CET had a higher median overall survival than endocrine therapy alone (65.7 versus 52.1 months, log-rank p-value&lt;.0001). However, further analysis noted that treatment with CET showed better outcome compared to ET alone in the following subgroups of patients: invasive ductal histology (95% OS 65.5 versus 52.7 months, log-rank p-value&lt;.0001) and RS &gt;30 (95% OS 63.6 versus 40.5 months, log-rank p-value&lt;.0001). Importantly, multivariable cox regression subgroup analysis revealed no significant overall survival difference among the subgroup of patients with T1b/T1c and low grade (p=0.286) or RS 26-30 (p=0.200) with CET compared to ET alone. Conclusions: This large database confirms the heterogeneity of BC in patients with low burden disease despite high Oncotype.While patients diagnosed with T1b/T1cN0M0 and high RS (&gt;30) could benefit from CET compared to ET alone as per standard practice, additional criteria could be considered in this group including low grade or RS 26-30 to better determine which population of patients do not benefit from the addition of chemotherapy and accordingly individualized chemotherapy decision might be made to minimize toxicity.