Blood-Based Genotyping of Colorectal Cancer Patients Transcript

Christina Lingham:
Hi, everyone. I'm Christina Lingham from the Next Generation DX Summit. I'm thrilled to have the opportunity to speak with Giulia Siravegna from the University of Torino on her lab's unique approach to employing circulating tumor DNA as a noninvasive biopsy. She will be presenting an update at the Next Generation DX Summit Clinical Application of Cell-Free DNA Conference taking place August 19 through 20 in DC. Giulia, thank you for joining us.

Giulia Siravegna:
Thank you.

Christina Lingham:
Can you describe your approach for the recent study on the potential of circulating tumor DNA in evaluating response to chemotherapy in colorectal cancer patients?

Giulia Siravegna:
Sure. Our study is based on previous evidences that tumor-derived DNA is fed into the bloodstream by cancerous cells. Although the presence of circulating tumor DNA in blood of patient has been updated now, only recent advances in genomics have allowed the detection and quantification of cancer-related molecular alteration with high specificity and sensitivity. Our group is actually interested in procedure medicine, and in particular, in colorectal patients. We initially realized that we could not understand the mechanism of acquired resistance to various therapies, like for example, the EGFR blockade with antigen for antibodies of BRAF inhibitors using only tissue biopsies for the inherent mutations.

In that case, we will not be able to interrogate the whole heterogeneic activity of the disease. We found that the tumor tissue, the genotyping of the tumor tissue will not comprehensively interrogate the heterogeneity of the disease, and so we move into this noninvasive approach, the liquid biopsy. We assessed whether the blood-based [inaudible 00:02:07] could be used to identify actionable targets to monitor drug resistance, and to track the tumor dynamic, and to do that, we'll use the PCR approach, that we built in our own institute, and we lately used in next generation sequencing approach to obtain more general profile of the circulating tumor DNA.

Christina Lingham:
Can you explain how circulating tumor DNA is most likely to be used by itself in conjunction with other tests in the standard of care for colorectal cancer?

Giulia Siravegna:
I think that the most likely application would be the monitoring of patients undergoing targeted therapies. The monitoring of the detection of the minimal residual disease with a more candidate approach. The diagnosis and the discovery of new actionable targets use NGS. Of course, the liquid biopsy approach should be coupled with the standard serum markers, and with the image approach, but of course, it will not completely replace the tissue biopsy for the reason, I was saying before, but of course, I hope it will be added side by side, and easily repeated many times with the standard approaches.

Christina Lingham:
What advice do you have from employing circulating tumor DNA in evaluating early therapeutic response?

Giulia Siravegna:
I think that the best way will be to collect serial blood draw during the treatment, and also right before the starting of the treatment because of the spike that we see in the very first weeks of treatment before the administration of the cycle one of the chemotherapy. This type has been proven to be an early indicator of response, and for sure it will be helpful for clinicians to consider to switch to another therapy, or to keep going with that therapy without the need of the CT scan evaluation.

Christina Lingham:
What are some of the most exciting applications emerging for liquid biopsies?

Giulia Siravegna:
I think that the most exciting ones are these heterogeneic assessment, the heterogeneic discovery of the complexities of the clone's dynamic in the tumor, and together, again, with the assessment of the minimal residual blood disease after surgery, and to decide whether the patient would need additional therapy, or if we can spare them the additional toxicity, and so on. We, for sure, will apply the liquid biopsy approach systematically in the frame of clinical trials in colorectal cancer patients first, but also in other setting like lung cancer, melanomas, pancreatic cancers. This will be helpful to monitor together with the clinician, how the clinical trial is going, and to have a more comprehensive view of the treatment benefit, and in order to be able to monitor virtually continuously the molecular revolution of the disease through the liquid biopsy.

Christina Lingham:
Giulia, tell us about the results from the recent liquid biopsy study published in Nature this week.

Giulia Siravegna:
We performed this very exciting study, and we found that circulating DNA could be used throughout the clinical arrangement of the colorectal cancer patient. In this way, we find a way to gather in real time, updates, on the molecular landscape of the disease. First we determined molecular profiles especially in using blood, and we assessed in concordance with the study between genotyping to blood, and the mesh tissue in over 100 patients, and then we applied the next generation sequencing technology to perform the analysis on the resistant patient, resistant to anti-EGFR therapy.

We found many alteration that were responsible for the acquisition of resistance, let's say, N-ras mutation, K-ras mutation, hetero complication, [meta 00:06:35] complication, and so on, also some novel EGFR extracellular mutation. We then followed patient after the acquisition of resistance, and we find that the K-ras clones actually declined in circulation when the selective pressure of the anti-EGFR antibody was withdrawn. This was very interesting also because those K-ras in the patient do not have any further lines of treatment when they acquire this mutation and resistance. It was very interesting to observe how these K-ras dropped down, and how this patient could be re-challenged with the same anti-EGFR therapy achieving, again, a clinical benefit.

Christina Lingham:
Lastly, what is unique about your approach? How did you become a leader in this field?

Giulia Siravegna:
We started the project in 2010, and I think, the best thing was that we've always believed in this approach, and because we believed that this approach would be very useful for patients, also to study the complexity of the colorectal cancer, but moreover for patients. Although we knew that working with circulating free DNAs is very challenging because it's very poor quality, it is not high as concentration in the circulation.

From a clinical point of view, it was very challenging, but with a five-year experience, now, we have built our own facilities with our own technologies, and we set up, as I was saying, the BEAMing technology, and we exploited other digital based PCR approach and the NGS with our own type of panel of 226 genes, which is able to capture, in sequence, the home-coding region of more than 200 genes. With our own efforts, we were able to analyze with a very high sensitivity and specificity to the circulating DNA. Of course, all of these would not be possible without the collaborators in a lot of hospitals in Italy and all over the world, and in particular with our collaborators in Niguarda Hospital in Milan, who provided patients and collected very carefully all the samples.

Christina Lingham:
Giulia, thank you for your time and insights today. That was Giulia Siravegna of the University of Torino. She'll be speaking at the Clinical Application of Cell-Free DNA at the Next Generation DX Summit taking place on August 19 through 20 in DC. I'm Christina Lingham, thank you for listening.