2019 ASCO Annual Meeting!
Session: Gastrointestinal (Colorectal) Cancer
Type: Poster Session
Time: Monday June 3, 8:00 AM to 11:00 AM
Location: Hall A
Circulating tumor DNA dynamics, serial testing and evolution on treatment in 322 colorectal cancer patients.
Gastrointestinal (Colorectal) Cancer
2019 ASCO Annual Meeting
Poster Board Number:
Poster Session (Board #58)
J Clin Oncol 37, 2019 (suppl; abstr 3566)
Author(s): Pashtoon Murtaza Kasi, Saivaishnavi Kamatham, Dorin Colibaseanu, Amit Merchea, Faisal Shahjehan, Jason Scott Starr, Kabir Mody; Mayo Clinic, Jacksonville, FL; University of Florida Health Cancer Center, Jacksonville, FL
Background: According to the American Society of Clinical Oncology and College of American Pathologists (ASCO/CAP) joint review on circulating tumor DNA (ctDNA) issued in March 2018, widespread use of ctDNA assays in most patients with advanced cancer is still an area of ongoing research. However, multiple studies thereafter published and/or presented support its use in patients with metastatic colorectal cancer (CRC). This has led to several institutions adopting it as ‘clinical practice’. The aim of this study is to report on our institution’s adoption of ctDNA testing for every patient at the time of diagnosis and/or time of progression. Methods: We report on results of 322 CRC patients with 607 ctDNA tests at our center from January 2017 to February 2019 using a commercially available platform (Guardant360). Results: Among 322 patients of our cohort, a total of 607 ctDNA tests were done (Table). 127 (39.4%) of these tests were serial analyses. In the CRC patients who had serial testing, at progression, mechanisms of resistance included acquisition of KRAS, NRAS, EGFR mutations; and HER2- and MET-amplifications. The subclonal mutations were noted to disappear when the selective inhibition was stopped. This was seen in patients on targeted therapies/biologics rather than chemotherapy. This was of value in treatment modification, clinical trial selection and/or monitoring of disease progression in these patients. Conclusions: While ctDNA testing may not be ready for primetime in all advanced cancers, it is increasingly being adopted in practice for especially metastatic CRC. Of particular value is the serial ctDNA testing in the RAS/RAF wildtype subset and now BRAF V600E mutant CRC on anti-EGFR based therapies.
|Total number of patients||322|
|Total number of tests||607|
|Number of serial analyses||127|
|RAS/RAF wild-type||214 (66.4%)|
|Number of RAS mutations||83 (25.8%)|
|Number of V600E BRAF mutations||18 (5.6%)|
|Number of non-V600EBRAF mutations||7 (2.2%)|
|Number of HER2 amplifications||13 (4%)|
|Number of HER2 mutations||7 (2.2%)|
*Of note, 25(7.8%) of CRC were dMMR/MSI-High in the cohort. CtDNA testing company started reporting MSI-High later in 3rd quarter of 2018.
1. Randomized phase III study comparing FOLFOX + bevacizumab versus folfoxiri + bevacizumab (BEV) as 1st line treatment in patients with metastatic colorectal cancer (mCRC) with ≥3 baseline circulating tumor cells (bCTCs).