Survival outcomes after pathologic complete response with neoadjuvant endocrine therapy vs. neoadjuvant chemotherapy: a retrospective national database study.

Background: Neoadjuvant therapies can result in pathologic complete response (pCR) in patients with breast cancer, which can be predictive of long-term outcomes. Patients with estrogen receptor positive (ER +) tumors may receive either neoadjuvant chemotherapy (NAC) or neoadjuvant endocrine therapy (NET). We sought to compare survival outcomes in those with non-metastatic ER + breast cancer who received NET or NAC and achieved pCR.

Methods: All patients diagnosed with ER + /HER2- stage I-III breast cancer, who received neoadjuvant systemic therapy followed by surgery, and achieved pCR, were selected from the National Cancer Database (NCDB, 2010-2021). The Kaplan-Meier method was used to estimate overall survival (OS), and log-rank tests were used to test for differences in OS. Cox Proportional Hazards models were used to estimate the association of NAC vs NET with OS, after adjustment for covariates.

Results: 3313 patients met eligibility criteria: 3148 received NAC and 165 NET. The median follow-up for the entire cohort was 82 months (95% CI 80.4-83.1). Patients who received NAC were significantly younger (median age: NAC 49y vs NET 64y; p < 0.001), more likely to have a comorbidity score of 0 (NAC 89.3% vs NET 81.2%, p = 0.004), and more likely to have private insurance (NAC 68.9% vs NET 44.2%, p < 0.001). There were no significant differences between the NAC and NET patients based on race and ethnicity, income, education, or community type (all p > 0.05). The NAC treated patients were more likely to have larger tumors [median tumor size (IQR): NAC 3 cm (2.0-4.3) vs NET 1.3 cm (0.7-2.8); p < 0.001)], ductal histology (NAC 92.6% vs 81.2%, p < 0.001), and grade 3 tumors (NAC 70.2% vs 10.3%, p < 0.001). In the unadjusted Kaplan-Meier analysis, there was no significant difference in OS between NAC vs NET [5-year OS: NAC 0.935 vs NET 0.916; p = 0.08]. After adjustment for demographics, disease characteristics, and treatments, there remained no association between OS and study group (NAC vs NET; p = 0.63).

Conclusions: Patients with ER + /HER2- early-stage breast cancer who achieved pCR had similar OS, regardless of whether they received NAC or NET. As such, pCR appears to have similar prognostic value irrespective of the type of systemic therapy used to obtain this favorable outcome.