Monitoring luminAl Breast Cancer Through the Evaluation of Mutational and epiGeNEtic alteraTIons of Circulating ESR1 DNA

The purpose of the study is to determine the diagnostic role of ctDNA when used to monitor metastatic breast cancer (MBC) during first-line endocrine therapy.

Patients with hormone receptor-positive MBC are eligible for endocrine therapy (ET) as first line treatment which is based on strategies aimed to either block signaling pathways depending on the estrogen receptor (ESR1) or using ESR1 antagonists. Only a few accepted predictive factors are associated with treatment benefit for MBC (i.e., hormone receptor status and HER2 status). Furthermore, a standardized assessment evaluation for MBC is still lacking. Because of these unmet needs, ET is continued until disease progression, or if toxicity requiring discontinuation occurs. Resistance is frequent in the treatment of early BC and unavoidable in MBC. Recently, mutations in ESR1 have been described in MBC that had been previously exposed to aromatase inhibitors (AIs) and are rarely detectable in primary BC. Besides that, resistance phenomena have been also linked to ESR1 cisregulatory elements (CRE, i.e. enhancers and promoters) hypermethylation, both related to ESR1 silencing. According to the literature, the aim of the study is to detect tumor response with liquid biopsy technique compared to conventional clinical pratice algorithms.