Circulating tumor cells (CTCs), the cells shed from a solid tumor into the bloodstream, may help doctors avoid having to do repeat needle biopsies on patients with unresectable non–small cell lung cancer.
Challenges to using CTCs clinically are that they are not abundant in the blood and have been difficult to isolate in patients with this type of cancer with commercially available assays.
In their paper, the authors show that an experimental nanotechnology can effectively isolate and measure CTCs in patients with stage 3 NSCLC. They also found that a precipitous drop in CTCs during chemoradiation treatment predicted significantly longer progression-free survival in those patients.
Study Results and Methods
For their research, study coauthors Shruti Jolly, MD, and Sunitha Nagrath, PhD, used a novel graphene oxide technology called the GO chip, developed more than a decade ago by Dr. Nagrath and her colleagues, to isolate CTCs from patients with stage 3 NSCLC. While a different technology, which is approved by the US Food and Drug Administration (FDA), uses a single antibody to pick up CTCs, the GO chip uses a cocktail of three antibodies to CTC proteins, making it more sensitive.
The 26 patients in the study (mean age 67, 27% female) all received radiation treatment for 6 weeks, plus weekly carboplatin and paclitaxel chemotherapy. Sixteen of the patients afterward went on to have immunotherapy with durvalumab. Blood was drawn at six fixed time points: before treatment, and at weeks 1, 4, 10, 18, and 30. CTCs were measured and analyzed with every draw.
Previous studies showed that absolute number of CTCs did not correlate with either tumor volume or progression-free survival in NSCLC.
Dr. Jolly and Dr. Nagrath sought to measure change in CTCs from baseline for each patient, having the patient serve as his or her own control. They found that patients whose individual CTC counts dropped by 75% or more between pretreatment and week 4 of chemoradiation saw a mean 21 months of progression-free survival compared with 7 months for patients whose CTCs dropped by less than 75% in the same period (P = .0076).
Dr. Jolly and Dr. Nagrath also aimed to determine, as an exploratory outcome of their study, whether other information collected from the CTCs could predict response to treatment with durvalumab immunotherapy. They found that having more than 50% of CTCs positive for the protein PD-L1 correlated to shorter progression-free survival among the 16 patients receiving durvalumab (P = .04).
“Every person’s tumor is unique in terms of its response to treatment,” said Dr. Jolly, a radiation oncologist and professor and associate chair of community practices in the Department of Radiation Oncology at the University of Michigan, Ann Arbor.
“Two people with a three-centimeter lung tumor will not necessarily shed the same amount of tumor cells into circulation. CTCs are reflective of disease burden; however, this is not related to the absolute numbers. That’s why we decided to use individualized baselines and look at the percentage of decrease,” she said.
Dr. Nagrath, professor of chemical and biomedical engineering at the University of Michigan, noted, in the same interview, that the findings argue for CTCs as a biomarker in stage 3 NSCLC.
“A lot of researchers who do lung cancer studies struggle with isolating lung cancer CTCs,” Dr. Nagrath said. “We showed, with repeated blood draws during treatment, what is changing at a molecular level and that you can see it with a simple blood draw. It also gives the proof of concept that if these cells are present, this is a good way to monitor and see if a treatment is working, even early in the treatment.” Moreover, she added, “many studies in lung cancer are in stage 4.”
Our study is unique as it followed patients with locally advanced tumors from their being treatment naive to all the way through immunotherapy,” she continued.
The University of Michigan has a patent on the GO chip technology, but thus far no company has made efforts to license it and submit it for approval. While “liquid biopsy” is an important emerging concept in lung cancer, there is little consensus yet as to which blood biomarkers — whether CTCs, circulating tumor DNA (ctDNA), or extracellular vesicles (EVs) — are most clinically relevant, Dr. Nagrath said.
The study’s small size is one of its weaknesses, according to the authors.