Abstract PS2-09: Next generation sequencing (NGS) in older adults with breast cancer using tissue-based and circulating tumor DNA (ctDNA) assays
Authors: Clifton Katherine K , Luo Jingqin , Tao Yu , Saam Jennifer , Rich Thereasa , Rearden Timothy , Roshal Anna , Frith Ashley , Rigden Caron , Ademuyiwa Foluso , Weilbaecher Katherine , Aya Leonel Hernandez , Peterson Lindsay , Bagegni Nusayba , Suresh Rama , Bose Ron , Wildes Tanya , Opyrchal Mateusz , Ma Cynthia 
Published: February 2021

Abstract
Background: With advances in next generation sequencing (NGS) and now approved targeted therapy in breast cancer, genomic testing to identify potentially actionable mutations has become a common practice in patients (pts) with advanced breast cancer using both ctDNA and traditional tissue-based assays. Less is known regarding physician practice patterns in obtaining NGS testing and the practical implications of testing in older adults with breast cancer.Methods: Pts with advanced breast cancer underwent molecular profiling using a plasma-based ctDNA NGS assay (Guardant360® or Tempus®) between 5/2015 and 5/2020 at Siteman Cancer Center. Pts with advanced breast cancer who underwent genomic profiling using a tissue-based NGS assay (Tempus®) between 12/2017 and 5/2020 at this institution were also included. Clinicopathological histories were obtained from the medical record. Correlations were examined using a Fisher’s exact test.Results: During 5/15-5/20, 244 pts underwent ctDNA testing and 147 pts had a tissue-based NGS assay performed. There was no significant difference between the number of pts ≥ 65 years-old who underwent ctDNA testing (n=78, 32.0%) and tissue testing (n=37, 25.2%). There was no statistically significant difference between date of metastatic diagnosis and date of NGS testing between the older and younger cohorts. In pts who underwent tissue-based NGS testing, there was no significant difference between site of tissue tested (distant recurrence vs local) in the older and younger cohorts. The most common clinical managements following both ctDNA and tissue-based testing are presented in Table 1. Out of the 391 pts who underwent testing, 27 pts had both ctDNA and tissue-based NGS performed. Pts ≥ 65 were less likely to have both assays performed (n=3, 11.1%; p&lt;0.05). In pts undergoing both assays, there were high concordance rates of ESR1 (81.5%) and PIK3CA (81.5%) mutations. Mean time between tissue and plasma collection for NGS testing in pts undergoing both assays was 356.4 days.
Conclusion: Older adults, who are typically less likely to be included in clinical trials, may still benefit from NGS to reveal potentially targetable mutations. It is reassuring in our cohort that older adults had ctDNA and tissue-based NGS performed at similar rates as part of standard of care treatment. The clinical management following NGS testing was also not significantly different in the older adult cohort. Older adults were less likely to have both tissue and ctDNA testing performed however, given the high concordance rates between tests, this may be less clinically relevant.
Table 1clinical management following NGS testing≥65 years-old&lt;65 years-oldp valueno actionable mutations41 (35.7%)123 (44.6%)p=0.1testing results saved for potential future use27 (23.5%)45 (16.3%)p=0.1change in management15 (13.0%)41 (14.9%)p=0.6
Citation Format: Katherine K Clifton, Jingqin Luo, Yu Tao, Jennifer Saam, Thereasa Rich, Timothy Rearden, Anna Roshal, Ashley Frith, Caron Rigden, Foluso Ademuyiwa, Katherine Weilbaecher, Leonel Hernandez Aya, Lindsay Peterson, Nusayba Bagegni, Rama Suresh, Ron Bose, Tanya Wildes, Mateusz Opyrchal, Cynthia Ma. Next generation sequencing (NGS) in older adults with breast cancer using tissue-based and circulating tumor DNA (ctDNA) assays [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS2-09.