A sensitive assay for circulating tumor DNA (ctDNA) in blood samples from patients being treated for their early non-small cell lung cancer (NSCLC) was found to be powerfully predictive of relapse after surgery in the LUCID-DNA study reported in the Annals of Oncology (2022; https://doi.org/10.1016/j.annonc.2022.02.007).
"These technologies are now getting close to-and are ready for-prime time. This type of information is available," said Nitzan Rosenfeld PhD, co-lead author of the study and group leader at the Cancer Research UK Cambridge Institute, University of Cambridge. "This allows you to get a much clearer picture of whether the patient has residual disease. Liquid biopsies allow you to ask questions about what actionable mutations there are for patients in advanced cancers."
The use of such minimally invasive tests to monitor low concentrations of ctDNA had opened up avenues to more refined treatment plans for dealing with early-stage cancer, Rosenfeld told Oncology Times. "Because we are going to improve the way we are dealing with early-stage cancer, this provides further rationale to increase the amount of screening in the population, because we have better tools for that as well," he said.
The Cambridge scientists developed a liquid biopsy assay called RaDaR that can analyze up to 48 different mutations in free DNA from the patient's blood circulation.
"Pre-surgery, we were able to identify and measure the levels of ctDNA in the majority of lung cancers, including the majority of patients with Stage I lung cancer. We were able to define the median levels of ctDNA in Stage I lung cancer: about 10 parts per million," said Rosenfeld, which gave a clear indication of sensitivities needed for new lung cancer screening tools.
"In the study, we start with a tumor analysis. We sequence the tumor by whole exome sequencing. We find-for each patient-a set of mutations which are a 'barcode' or 'fingerprint' representative of the cancer. And we develop-for each patient-an assay that's tailored for that patient," he noted. "Now we're looking [for every patient] for 48 different mutations that are unique to that patient."
The individualized RaDaR assays were used to detect ctDNA in 363 plasma samples taken from 88 patients with early-stage NSCLC. Analysis of liquid biopsies before and after treatment showed that ctDNA had been present in just over half of all patients (51%) before initial treatment and in nearly two-thirds of patients who had a relapse (64.3%) after treatment.
"When we looked for very minimal residual ctDNA after surgery, we found that when we detect ctDNA in the few weeks or months after surgery these patients invariably went on to have a relapse of their cancer, unfortunately, within 1-2 years."
The converse, however, was not true, said Rosenfeld: "The patients in whom we do not detect ctDNA-unfortunately, we are not able to give them a complete all-clear signal. Some of them do relapse. But they have a much better prognosis."
Because patients who tested positive for ctDNA at a so-called "landmark timepoint" after treatment had shorter recurrence-free and overall survival times, the researchers concluded that detection of minimal residual disease after treatment for early-stage NSCLC identified patients for further intervention.
This was a significant and powerful step forward, according to Rosenfeld. "We are not trying to predict the future on the basis of the characteristics of the cancer that's been taken out. We're looking in the blood. And when we see these tumor-specific mutations still in the blood, it's really a clear sign that tumor is still present in the body."
Study Origins
In earlier genomic research, the study group had already been able to explore what had been the ctDNA landscape in early-stage lung cancers, said Rosenfeld. "We already had a glimpse that in advanced cancers we were able to detect quite large levels of ctDNA in the blood. And we were curious to see how low these levels would be in early-stage lung cancer. So, we set out to collect samples from patients before surgery, after surgery, and during follow-up to see the levels. Could we detect them? And would there be anything of clinical value from that collection?"
Rosenfeld noted that the assay was not suitable for cancer screening because it targeted genomic variants on each patient's individual tumor. In the absence of a tumor, a different set of molecular targets were needed for the population at large.
Study Details
In the study, the researchers analyzed serial plasma samples from patients with early-stage cancers (treated with curative intent) by surgery (61 patients), surgery and adjuvant chemotherapy/radiotherapy (8 patients), or chemoradiotherapy (19 patients). Tumor exome sequencing identified somatic mutations, and the plasma was then analyzed using patient-specific RaDaR assays with up to 48 amplicons targeting tumor-specific variants unique to each patient.
ctDNA of a few parts per million was found before treatment in 24 percent of patients with Stage I disease, 77 percent of patients with Stage II disease, and 87 percent of those with Stage III NSCLC. It was also detected in 26 percent of all longitudinal samples.
After treatment, ctDNA was detected in 18 out of 28 (64.3%) of patients who had clinical recurrence of their primary tumor. It had a clinical specificity of more than 98.5 percent. RaDaR detection preceded clinical detection of recurrence of the primary tumor by a median of 212.5 days.
Detection within the chosen landmark timepoint (from 2 weeks to 4 months after treatment end) occurred in 17 percent of patients and was associated with shorter recurrence-free survival (HR: 14.8; P<0.00001) and overall survival (HR: 5.48, P<0.0003). ctDNA was detected from 1-3 days after surgery in a quarter of patients, but was not associated with disease recurrence. The large hazard ratios prompt confidence in the power of the RaDaR test as a predictive tool. Detection before treatment was associated with shorter overall survival (HR: 2.97, P value below 0.01 ) and recurrence-free survival (HR: 3.14; P value below 0.003).
The LUCID-DNA researchers concluded that ctDNA detection after initial treatment of patients with early-stage NSCLC using sensitive patient-specific assays had potential to identify patients who may benefit from further therapeutic intervention.
Peter M. Goodwin is a contributing writer.