Abstract LB-224: Circulating tumor DNA for early detection and intervention in breast cancer: ctDNA profiles discriminate between healthy women in a true cancer screening setting and disease-free women on follow up
Authors: Shaw Jacqui A. , Page Karen , Fernandez-Garcia Daniel , Hills Allison , Boydell Anna R. , Primrose Lindsay , Toghill Bradley , Hastings Robert K. , Gleeson Kelly , Rosales Brenda M. , Goddard Kate , Guttery David S. , Ali Simak , Coombes Raoul C. 
Published: August 2018

Abstract
Successful early detection and intervention in cancer is key if we are to drastically improve cancer survivorship. Previous research by us and others has shown that copy number and mutational profiling of circulating cell-free DNA (cfDNA) can detect minimal residual disease and predict who will relapse after early stage breast cancer (Shaw et al. Genome Res 2012, doi: 10.1101, Garcia-Murillas et al. Sci Transl Med. 2015 doi: 10.1126). Here we used massively parallel sequencing with the Ion CHEF -S5 and Oncomine™ Breast cfDNA Assay (Thermofisher) for ultrasensitive detection of circulating tumour derived DNA (ctDNA) in 26 asymptomatic early stage breast cancer patients with no scan evidence of distant metastases on follow up after surgery, (all of whom were receiving adjuvant AI (PAI) at the time of blood sampling). We compared these early stage breast cancers with cfDNA isolated from 40 patients with metastatic breast cancer (MBC) and 92 healthy age matched female controls (HC) attending for a routine breast screening mammogram. The Oncomine™ Breast cfDNA Assay targets &gt;150 hotspot mutations in 10 breast cancer genes and uses tag sequencing technology to achieve a limit of detection (LOD) down to 0.1%. One or more driver mutations were detected in cfDNA of 19 (73%) PAIs and 29 (72.5 %) MBCs, whereas just 15 HCs (16%) were positive. Applying this threshold of 1 or more driver mutations for detection of ctDNA (Cohen et al. Science. 2018 doi: 10.1126) there was a significant difference between ctDNA positive cancers and healthy controls, which also remained significant for 2 or more driver mutations (P &lt; 0.0001 and P &lt; 0.001 respectively, Fisher's exact test) (Abbosh et al. Nature 2017, doi: 10.1038). It is notable that &gt;72% of breast cancers were positive with this test, both disease-free women on follow up and patients with MBC, suggesting a role for the test in routine monitoring. A second finding of clinical significance was that variant allele fraction of ESR1 mutant ctDNA was significantly higher in cancers than controls (PAIs than HCs (P = 0.034) and MBCs than HCs (P = 0.002); adjusted P value, Dunn's multiple comparison test) suggesting that ESR1 mutations distinguish disease-free breast cancer survivors receiving adjuvant aromatase inhibitors from normal women. Importantly, we are the first to report ultrasensitive evaluation of ctDNA alterations in a large number of healthy women in a true cancer screening setting. The 15 healthy women that were “positive” for ctDNA may be harbouring an early stage cancer not detectable by imaging. Research is ongoing to validate these results in a larger study, but our results suggest that the approach may have utility for early disease detection and monitoring to enable appropriate intervention at earlier stages.
Citation Format: Jacqui A. Shaw, Karen Page, Daniel Fernandez-Garcia, Allison Hills, Anna R. Boydell, Lindsay Primrose, Bradley Toghill, Robert K. Hastings, Kelly Gleeson, Brenda M. Rosales, Kate Goddard, David S. Guttery, Simak Ali, Raoul C. Coombes. Circulating tumor DNA for early detection and intervention in breast cancer: ctDNA profiles discriminate between healthy women in a true cancer screening setting and disease-free women on follow up [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr LB-224.