The impact of recurrence score (RS) performed on pretreatment (Tx) core biopsies (CB) in predicting response to neoadjuvant chemotherapy (NCT) in patients (Pts) with ER+ breast cancer (BC).

Abstract

63 Background: The Oncotype DX 21-gene assay is beneficial in predicting disease-free survival and local regional relapse in hormone receptor BC. The ability of the assay to predict response of primary BC to NCT is less well studied. We hypothesize a (+) association exists between the RS result on pre-Tx CB and % tumor response (%TR) after NCT on final pathology. Methods: Pre-Tx RS was measured on paraffin-embedded CB from 60 pts with ER+ Her2(-) BC who then received NCT and for whom post-Tx pathology was available. %TR is calculated as 100 x (pre-Tx size – post-Tx size)/pre-Tx size. Pre-Tx tumor size was determined using imaging measurements selected in the following preferential order: MRI, US or mammogram. Post-Tx tumor size was calculated as the product of: maximum dimension of tumor-bed/fibrosis and % change in cellularity (compared with pre-therapy biopsy). Partial response (PR) is defined as ≥50% reduction in TR. Results: Mean pre-Tx tumor sizewas 4.8 (range 1-23) cm. 83% of pts were clinically lymph node (-). Nottingham Score was >6 in 93%. Breast conserving surgery was performed in 17 (28%) pts. Median RS was 20 (range 3-69). Median %TR was 42 (range 0-97)%. There were no pCRs. PR was observed in 43% of pts. No association was found between %TR and pre-NCT tumor size, age, Nottingham score or node status (p>0.05). No association for the RS as a continuous or categorical variable with %TR (p>0.05) was seen. There is a non-significant (p=0.07) trend toward increased response to NCT with increasing RS. Response to NCT improved as values of ER (p=0.02) and HER2 (p=0.007), by RT-PCR as reported with the RS, decreased. Conclusions: In the subset of patients with ER+ BC, where NCT was recommended to affect tumor downstaging, RS did not successfully discriminate pts that would respond to NCT as measured by %TR. While there was a trend toward better response with higher scores, the result was nonsignificant. The use of this genetic assay to discriminate between NCT and hormonal therapy requires further study. [Table: see text]