Genomic comparison of paired primary breast carcinomas and lymph node macrometastases using the Oncotype DX Breast...

Adjuvant therapy decisions may in part be based on results of Oncotype DX Breast Recurrence Score^® (RS) testing of primary tumors. When necessary, lymph node metastases may be considered as a surrogate. Here we evaluate the concordance in gene expression between primary breast cancers and synchronous lymph node metastases, based on results from quantitative RT-PCR-based RS testing between matched primary tumors and synchronous nodal metastases.

This retrospective, exploratory study included patients (≥ 18 years old) treated at our center (2005-2009) who had ER+ , HER2-negative invasive breast cancer and synchronous nodal metastases with available tumor blocks from both sites. Paired tissue blocks underwent RS testing, and RS and single-gene results for ER, PR, and HER2 were explored between paired samples.

A wide distribution of RS results in tumors and in synchronous nodal metastases were modestly correlated between 84 paired samples analyzed (Pearson correlation 0.69 [95% CI 0.55-0.78]). Overall concordance in RS group classification between samples was 63%. ER, PR, and HER2 by RT-PCR between the primary tumor and lymph node were also modestly correlated (Pearson correlation [95% CI] 0.64 [0.50-0.75], 0.64 [0.49-0.75], and 0.51 [0.33-0.65], respectively). Categorical concordance (positive or negative) was 100% for ER, 77% for PR, and 100% for HER2.

There is modest correlation in continuous gene expression, as measured by the RS and single-gene results for ER, PR, and HER2 between paired primary tumors and synchronous nodal metastases. RS testing for ER+ breast cancer should continue to be based on analysis of primary tumors.