This was the main finding of new data presented by study author Razelle Kurzrock, MD, at the American Association for Cancer Research annual meeting.
“We found that on-treatment ctDNA can detect progression before standard-of-care response assessments. These data suggest that monitoring ctDNA can provide clinicians with important prognostic information that may guide treatment decisions,” Dr. Kurzrock, professor at the Medical College of Wisconsin, Milwaukee, said during her presentation.
Christos Evangelou/MDedge News
Dr. Razelle Kurzrock
Commenting on the clinical implications of these findings during an interview, she said the results suggest that ctDNA dynamics provide an early window into predicting response to targeted therapies in patients with HER2-altered cancers, confirming previous findings of the predictive value of ctDNA in other cancer types.
“Such monitoring may be useful in clinical trials and eventually in practice,” she added.
Need for new methods to predict early tumor response
Limitations of standard radiographic tumor assessments present challenges in determining clinical response, particularly for patients receiving targeted therapies.
During her talk, Dr. Kurzrock explained that although targeted therapies are effective for patients with specific molecular alterations, standard imaging assessments fail to uncover molecular-level changes within tumors, limiting the ability of clinicians to accurately assess a patient’s response to targeted therapies.
“In addition to limitations with imaging, patients and physicians want to know as soon as possible whether or not the agents are effective, especially if there are side effects,” Dr. Kurzrock during an interview. She added that monitoring early response may be especially important across tumor types, as HER2 therapies are increasingly being considered in the pan-cancer setting.
Commenting on the potential use of this method in other cancer types with HER2 alterations, Pashtoon Murtaza Kasi, MD, MS, noted that since the study relied on a tumor-informed assay, it would be applicable across diverse tumor types.
“It is less about tissue type but more about that particular patient’s tumor at that instant in time for which a unique barcode is created,” said Dr. Kasi, a medical oncologist at Weill Cornell Medicine, New York, who was not involved in the study.
In an interview, he added that the shedding and biology would affect the assay’s performance for some tissue types.
Design of patient-specific ctDNA assays
In this retrospective study, the researchers examined ctDNA dynamics in 58 patients with various HER2-positive tumor types, including breast, colorectal, and other solid malignancies harboring HER2 alterations. All the patients received combination HER2-targeted therapy with trastuzumab and pertuzumab in the phase 2 basket trial My Pathway (NCT02091141).
By leveraging comprehensive genomic profiling of each patient’s tumor, the researchers designed personalized ctDNA assays, tracking 2-16 tumor-specific genetic variants in the patients’ blood samples. FoundationOne Tracker was used to detect and quantify ctDNA at baseline and the third cycle of therapy (cycle 3 day 1, or C3D1).
During an interview, Dr. Kurzrock explained that FoundationOne Tracker is a personalized ctDNA monitoring assay that allows for the detection of ctDNA in plasma, enabling ongoing liquid-based monitoring and highly sensitive quantification of ctDNA levels as mean tumor molecules per milliliter of plasma.
Among the 52 patients for whom personalized ctDNA assays were successfully designed, 48 (92.3%) had ctDNA data available at baseline, with a median of 100.7 tumor molecules per milliliter of plasma. Most patients (89.6%) were deemed ctDNA-positive, with a median of 119.5 tumor molecules per milliliter of plasma.