Whole transcriptome analysis comparing HR+ HER2- breast cancer tumors from patients < 50 years and >50 years.
Authors: Graham Cathy , Marks Douglas Kanter , D'Abreo Nina , Diab Sami , Gadi Vijayakrishna K. , Kuilman Midas , Menicucci Andrea , Truitt Amy Michelle , Wang Shiyu , Audeh William ,   FLEX Investigators' Group
Published: June 2021

565 Background: Recent prospective clinical trials have demonstrated a differential chemotherapy effect based on age (≤ 50 vs. > 50 years) or menopausal status (pre- vs. post-) in a genomic low risk group. Whether this is a direct anti-tumor effect of chemotherapy or a secondary ovarian function suppression effect caused by chemotherapy is unclear. We aimed to compare the biological characteristics of breast cancer tumors from patients aged ≤ 50 years and from patients aged > 50 years using whole transcriptome analysis to provide insights into this differential chemotherapy response. Methods: The FLEX Registry (NCT03053193) enrolls stage I-III breast cancer patients who receive 70-gene signature (MammaPrint/MP) test with or without 80-gene signature (BluePrint/BP) test and consent to clinically annotated transcriptome data collection. 3868 patients with HR+HER2- tumors were evaluated, of whom 808 were aged ≤ 50 years and 3060 were aged > 50 years. Clinical risk was assessed based on the MINDACT algorithm. MP classified tumors as low risk (LR) or high risk (HR). HR was stratified to H1 or H2; H2 exhibits a greater chemotherapy response. BP and MP classified tumors as luminal A-, luminal B-, HER2-, or basal-type. Differences in MP, BP, and clinical features were assessed by chi-squared or t test. For gene expression analysis, older patients were randomly selected to obtain an equal sample size as younger patients. Differentially expressed genes (DEGs) were detected using limma and considered significant with FDR <0.05 and fold change ≥ 2. Results: Approximately 70% of patients aged ≤ 50 were pre or peri-menopausal, whereas 90% of patients aged > 50 were post-menopausal. A higher proportion of patients aged ≤ 50 had tumors of high clinical risk (54%) compared to patients aged > 50 (39%) (p < 0.001). Approximately 53% of patients aged ≤ 50 had a HR tumor, of whom 25% classified as H2, while patients aged > 50 had a lower frequency (44%) of HR tumors (p<0.001). Additionally, younger patients had more tumors that classified as BP Luminal B and Basal-type than older patients (p<0.001). Principal component analysis of the top 500 genes with the highest variance revealed no distinct clustering by age group. Accordingly, only 5 DEGs were detected in tumors from patients aged ≤ 50 compared to patients aged > 50, and even fewer DEGs were detected when adjusting for MP risk and BP subtype group. Conclusions: Whole transcriptome analysis identified no substantial differences in gene expression between tumors, including Low Risk Luminal-type tumors, from women aged ≤ 50 (mostly pre or peri-menopausal) and women aged > 50 (mostly post-menopausal). These data support the likely explanation that the observed age-dependent difference in chemotherapy benefit in women ≤ 50 or >50 years of age is not due to intrinsic biological differences in breast cancers due to age, but rather to differences in the effect of chemotherapy on the host. Clinical trial information: NCT03053193.