Bone metastatic biopsies of breast cancer patients progressing on endocrine therapies.

A significant proportion of patients with ER positive breast cancers (BC) develop resistance to endocrine treatments (ET) and relapse with metastatic disease. Bone is the most common metastatic site in ER+ patients, however bone metastases are technically challenging to biopsy and analyse. Difficulties concern both tumour tissue acquisition and techniques for analysis and RNA extractions. Patient-derived xenografts (PDX) of BC bone metastases have not been reported yet. For the first time we established PDX models from bone metastatic biopsies of patients progressing on ET and treated by vertebroplasty. PDX models were analysed at genomiclevel and compared to patient’s early primary tumours to identify new therapeutic targets associated with endocrine resistance in the metastatic setting.EGA study EGAS00001004268