581 Background: While neoadjuvant chemotherapy (NACT) has been established as the standard of care for medically fit patients, there has been renewed interest in utilizing neoadjuvant endocrine therapy (NET) for the treatment of women with estrogen-receptor (ER) positive, HER-2 negative breast cancer. Rates of pCR are known to be low in this population, but there is inconsistent data regarding downstaging and long-term outcomes in a non-trial setting with NET vs NACT. Methods: A prospective institutional databaseof breast cancer patients treated with neoadjuvant therapy at the British Columbia Cancer Agency from 2012-2016 was analyzed to identify all medically fit patients with ER positive, HER2 negative breast cancer. Patients were then divided into two groups: those who received NET or NACT. Baseline characteristics were compared between groups. A matched analysis (age, stage and grade) was then performed to compare rates of downstaging, pCR and scores from a validated neoadjuvant therapy outcomes calculator (CPS+EG). Results: A total of 154 patients met eligibility criteria for this study. One hundred and six patients (69%) received NACT and 48 (31%) received NET. Women offered NACT were significantly younger (51 vs 64y, p < 0.001) than those offered endocrine therapy and presented with a higher clinical stage (LR 27.93, p = 0.002). According to multiple linear regression for downstaging, clinical stage followed by NACT were the most important predictors of downstaging. When matched for age, stage and grade, downstaging was significantly higher with NACT (31/48, 65%) as compared to NET (12/48, 25%), p < 0.001. Of these, 12.5% achieved pCR with NACT as compared to 2.1% with NET, LR 4.243, p = 0.039. No significant differences in CPS+EG scores were identified when comparing NACT to NET. Conclusions: Significantly higher rates of downstaging were achieved with NACT as compared to NET when patients were matched for age, stage and grade. Rates of pCR remain low for ER-positive breast cancer patients. Although not validated with the use of NET, CPS+EG scores predicting long-term outcomes were not significantly different with NET compared to NACT.
Long-term outcomes following adjuvant endocrine therapy in breast cancer patients with a positive-to-negative change of hormone receptor status following neoadjuvant chemotherapy