Abstract P5-11-03: Measurement of on-treatment proliferation biomarkers in nodal metastasis improves prediction of endocrine therapy response using the EA2CliN test
Authors: Turnbull AK , Mok S , Martinez-Perez C , Fernando A , Renshaw L , Keys J , Sims AH , Dixon JM 
Published: May 2019

Background: The majority of patients with early-stage estrogen receptor positive (ER+) breast cancer (BC) are treated with adjuvant endocrine therapy (ET) after surgery to reduce the risk of recurrence. Recently, we have developed and validated an immunohistochemistry (IHC) based assay (EndoAdjuvant2 Clinical; EA2Clin) that measures pre-treatment IL6ST level together with clinical variables and on-treatment MCM4 to assess proliferation. We have previously shown that it can accurately identify responders and non-responders to ET and predicts recurrence-free survival (RFS) and BC-specific overall survival (BCSS). We postulated that measuring on-treatment proliferation in lymph node metastases (LN+) rather in the primary cancer might further improve the accuracy of the test for these patients. The aim was to test and validate this in cohorts of pre- and post-menopausal women (preMW & PMW) treated with preoperative ET (tamoxifen (T), fulvestrant (F), letrozole (L) or anastrozole (A)) and subsequent adjuvant ET.

Methods: Cohorts: (1) 137 PMW with ER+ BC, 59 were LN+, treated with neoadjuvant L (median duration 4.8 months, range 1-33), then surgery followed by adjuvant L (n=109) or other ET (n=28); (2) 148 PMW with ER+ BC, 55 were LN+, treated with 2 weeks of preoperative L (n=76) or A (n=72), then surgery followed by adjuvant L (n=69) or T (n=79); (3) 52 preMW with ER+ BC, 24 were LN+, treated with 2 weeks of preoperative T (n=26) or 1x750mg dose of F (n=26), then surgery followed by adjuvant T. All LN+ patients had sentinel node biopsies or clearance. The median follow-up was 6.5 years (cohort 1), 6.3 years (cohort 2) and 10.2 years (cohort 3).

EA2Clin: Patients are classified as:

· Low risk: ER+ and LN-negative and &lt;2cm or pre-treatment IL6ST 2+/3+ (IHC) and post-treatment MCM4 in the primary has &lt;20% positive nuclear staining.

· High risk: ER+ LN+ grade 3 BCs &gt;2cm or pre-treatment IL6ST is 0 or 1+, or IL6ST is 2+ or 3+ and MCM4 in the primary has &gt;10% positive nuclear staining.

EA2CliN uses the post-treatment level of MCM4 in the nodes, rather than the primary cancer.

Results: In cohort 1, EA2Clin (using primary tumour MCM4) was significantly associated with both RFS (P=0.0003, HR=13.17, 95%CI=5.48-13.61) and BCSS (P=0.005, HR=11.91, 95%CI=8.73-31.42). The 5 and 10 year actuarial recurrence rates were 5%/5% and 48%/64% for the low and high-risk groups respectively.

In the same cohort, using the MCM4 level in the node (EA2CliN) there was an even more significant association with both RFS (P&lt;0.00009, HR=18.16, 95%CI=12.59-19.46) and BCSS (P=0.002, HR=12.93, 95%CI=5.43-25.62). The 5 and 10 year actuarial recurrence rates were 0%/0% and 48%/72% for the low and high-risk groups respectively. Further validation of EA2CliN in cohorts 2 and 3 is underway.

Discussion:

· Direct measurement of on-treatment proliferation biomarkers in LN metastases improves prediction of outcomes to ET in women with BC.

· This tests identifies a group of low risk women that are node negative and node positive with a 100% RFS and BCSS.

· This is the most impressive predictive test for patients with ER+ breast cancer yet developed.

Citation Format: Turnbull AK, Mok S, Martinez-Perez C, Fernando A, Renshaw L, Keys J, Sims AH, Dixon JM. Measurement of on-treatment proliferation biomarkers in nodal metastasis improves prediction of endocrine therapy response using the EA2CliN test [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P5-11-03.