Abstract P4-04-02: Characterising the effects of neoadjuvant endocrine therapy on primary cancers and nodal metastasis
Authors: Dixon JM , Turnbull AK , Tanioka M , Parker J , He X , Fernando A , Renshaw L , Keys J , Thomas JS , Sims AH , Carey LA , Perou CM 
Published: February 2018

Background: Approximately 40% of ER+ breast cancer present with nodal metastasis. To date, there has been no comparison of the molecular response of primary cancers and metastases to ET. Recent evidence suggests that nodal metastases have different clones and subclones compared to the primary tumour. The aim of this study is to characterise the molecular response of primaries and nodal metastases to ET.

Methods: A unique set of 7 post-menopausal women with ER-positive breast cancer had biopsies taken from the primary tumour and a positive lymph node at diagnosis and at surgery following 3-12 months of neoadjuvant letrozole. 14-day and 3-6 month on-treatment biopsies from the primary tumour and involved nodes were also taken from the same patients, giving a total of 75 samples. Lymph node FFPE blocks were stained for cytokeratin and macro-dissected to enrich for tumour tissue. RNA and DNA were extracted and Ribo0-RNAseq, DNA exome sequencing and somatic mutation detection using UNCeqR performed. Whole-transcriptome AmpliSeq targeted-sequencing has been analysed for 4 patients.

Results: Multi-dimensional scaling and hierarchical clustering analysis based on all transcripts and the 500 most variably expressed genes revealed that primaries and nodal metastases are strongly associated at diagnosis but some nodes diverge during ET treatment. Analysis of estrogen-responsive proliferation-associated genes (n=60) in nodal metastasis revealed a reduction in expression of the majority of genes with ET. However, the expression levels of some remained high in the on-treatment node samples in all 4 patients analysed compared with the matched primary tumour on treatment. In particular, expression of genes involved in DNA replication and regulation of cell cycle including MCM6 and RRM2 (DNA replication), ASPM and CEP55 (mitosis) and CDKN3 (regulation of cell cycle) persisted at high levels in nodal metastases, but reduced in the primary cancers. Similarly, primary tumours had increased levels of ECM remodeling genes (n=60) as treatment continued, while levels in the nodal metastasis were heterogeneous on-treatment. Full genome sequencing results will be available by December 2017.

Discussion

· This is the first study to investigate genomic and transcriptomic changes with ET in both primary cancers and nodal metastases.

· On-treatment changes in nodal disease are heterogeneous between patients and within the same patient.

· Nodal metastases do respond to ET with reduced levels of proliferation-associated genes.

· Some proliferation-associated genes appear to maintain higher expression in nodal disease.

· Patterns of gene expression observed in some nodal metastases are consistent with profiles previously described by us for ET resistance and recurrent disease.

· Nodal metastases may accumulate mutations during treatment with ET and on-going analysis will clarify this.

Citation Format: Dixon JM, Turnbull AK, Tanioka M, Parker J, He X, Fernando A, Renshaw L, Keys J, Thomas JS, Sims AH, Carey LA, Perou CM. Characterising the effects of neoadjuvant endocrine therapy on primary cancers and nodal metastasis [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P4-04-02.