Abstract
e23047 Background: Though 93% of patient present with early stage breast cancer (EBC), metastatic recurrence is expected in 7-13%. To prevent estrogen receptor (ER) positive disease recurrence, endocrine therapy (ET) is given after local disease. ET guidelines recently extended therapy —specifically tamoxifen—from 5 years to 10 based on ATLAS and aTTom. This pilot study used blood samples from women 6 months post-ET to determine cell free DNA (cfDNA) mutation prevalence in disease-free patients Methods: Patients with EBC and continued follow-up after ET were recruited from the Magee Women’s Breast Cancer Clinic. Inclusion criteria were EBC, ER+, and completion of ET > 6 months prior to visit; the exclusion criterion was active disease. Patients gave 2 blood samples, placed in Streck and EDTA tubes and processed at 2 laboratory sites for cfDNA. Blood from patients with metastatic breast cancer (MBC) served as controls for mutation detection. cfDNA was amplified for ESR1 and PIK3CA genes. Targeted amplifications underwent digital droplet PCR to identify mutations: 4 for ESR1 (D538G, Y537C/N/S), 2 for PIK3CA (E545K, H1047R) Results: Ten EBC patients > 6 months post-ET (post-EBC; 2/5/3 of stage I/II/III) and 10 MBC patients gave samples. cfDNA yield between plasma isolated from EDTA and Streck tubes (including mutation allele frequencies) was not significantly different (p > 0.05); cfDNA yield from patients with MBC was > 2X higher than post-EBC (p < 0.001). MBC cfDNA had 2 monoclonal and 1 polyclonal (2 different) mutations in ESR1, while post-EBC cfDNA had none Conclusions: This pilot study shows cfDNA can be consistently isolated from Streck or EDTA-processed blood from patients with MBC and post-EBC; however, cfDNA levels are significantly higher in MBC. There were no mutations (ESR1 or PIK3CA) in post-EBC samples, though ESR1 mutations were found in MBC. Further studies are needed to determine if mutations in cfDNA can be found in patients without evidence of disease
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