Sensitive detection and functional analysis of esr1 mutations in metastatic breast cancer

Given the clinical relevance of ESR1 mutations as potential drivers of resistance to endocrine therapy, in our first study we used sensitive detection methods to determine the frequency of ESR1 mutationsin primary and metastatic breast cancer, and in cell-free DNA (cfDNA). Six ESR1 mutations (K303R, S463P, Y537C, Y537N, Y537S, D538G) were assessed by digital droplet PCR (ddPCR), with lowerlimits of detection of 0.05% to 0.16%, in primary tumors (n=43), bone (n=12) and brain metastases (n=38), and cfDNA (n=29). Correlations between ESR1 mutations in metastatic lesions and single (1patient) or serial blood draws (4 patients) were assessed. ESR1 mutations were detected for D538G (n=13), Y537S (n=3), and Y537C (n=1). Mutation rates were 7.0% (3/43 primary tumors), 9.1% (1/11bone metastases), 12.5% (3/24 brain metastases), and 24.1% (7/29 cfDNA). Two patients showed polyclonal disease with more than one ESR1 mutation. In cases with both cfDNA and metastaticsamples (n=5), mutations were detected in both (n=3) or in cfDNA only (n =2). Treatment was associated with changes in ESR1 mutation detection and allele frequency.In our second study, weperformed genome editing using CRISPR and adeno-associated virus (AAV) technologies to knock-in ESR1 mutations into T47D and MCF7 cell lines, respectively. Various techniques were utilized toassess the activity of mutant ER. Cells with ESR1 mutations displayed ligand-independent ER activity, and were resistant to several SERMs and SERDs, with cell line and mutation-specific differences withrespect to the magnitude of the effect.Taken together, we prove that ESR1 mutations could be detected at very low allele frequencies in some primary breast cancers, and at high allele frequency in metastases, suggesting that in some tumors rare ESR1-mutant clones are enriched by endocrine therapy. This is of great clinical importance as detection of such mutations could potentially change the course of therapy in breast cancer patients. Our functional study of ESR1 mutations confirms the ligand-independent and drug resistance activity of mutant cells in genome edited models.

کلیدواژه ها:

Breast Cancer ، Cancer Diagnosis ، Liquid Biopsy and Cancer ، Solid Tumors ، Drugs and Cancer