Impact of genomic assays on treatment and outcomes in locally advanced breast cancer

Purpose: Genomic profiling in early-stage breast cancer provides prognostic and predictive information. Genomic profiling assays have not been validated in locally advanced breast cancer (LABC). We examined a large cancer registry to evaluate genomic profiling in LABC and its effect on treatment decisions and survival. Methods: Females with ER+/HER2− LABC who did not receive neoadjuvant therapy were selected from the National Cancer Database 2004–2017. We compared characteristics between patients with and without genomic profiling and with low genomic risk, 21-gene recurrence score ≤ 25 or low-risk 70-gene signature, treated with endocrine therapy ± chemotherapy. Propensity score methods were utilized to account for covariates that may have predicted treatment. Univariable and multivariable survival analyses were performed. Results: Of 18,437 patients with LABC, 1258 (7%) had genomic profiling and 1022 (81%) had low genomic risk results. 562 patients (55%) with low genomic risk received chemotherapy and endocrine therapy (chemoendocrine). Patients who received chemoendocrine therapy were younger, had fewer comorbidities, presented with higher stage disease, had higher grade tumors, more frequently had partial mastectomy, and more often received radiation than those who received endocrine therapy alone. On multivariable analysis, endocrine therapy alone was associated with worse OS compared to chemoendocrine therapy (HR 1.77, 95% CI 1.13–2.78, p = 0.013). Conclusion: In women with LABC and low genomic risk, endocrine therapy alone was associated with worse OS compared to chemoendocrine therapy. This suggests that genomic profiling is not predictive in LABC. Accordingly, genomic profiling should not be routinely utilized to make adjuvant treatment decisions in LABC in the absence of further data which shows a benefit.