Dr. Manish Shah (Host): Welcome to Weill Cornell Medicine CancerCast, conversations about new developments in medicine, cancer care, and research. I'm your host, Dr. Manish Shah. And today, we will be talking about liquid biopsies and how this technology is used in cancer care.

Our guest today is Dr. Massimo Cristofanilli. Dr. Cristofanilli is an internationally recognized medical oncologist, investigator, and researcher at Weill Cornell Medicine/NewYork-Presbyterian Hospital. He serves as the Associate Director of Precision Oncology at the Meyer Cancer Center, as well as the Scientific Director of the Englander Institute for Precision Medicine. Dr. Cristofanilli's research focuses on biomarkers of endocrine resistance in breast cancer, liquid biopsies, and novel drug development. Massimo, welcome.

Dr. Massimo Cristofanilli: Thank you, Manish. I'm glad to be here.

Dr. Manish Shah: So, today's topic is really dear to our heart, because it feels very cutting-edge, the ability to take a blood sample and learn a lot about someone's tumor. It would be great to have a discussion with you about what this means and where we can go in the future. There's this idea that we can do a liquid biopsy versus a tumor biopsy or a traditional biopsy. Can you tell us what the difference is between liquid biopsy and a regular biopsy?

Dr. Massimo Cristofanilli: Tissue biopsy has been the gold standard or the traditional way to assess, first of all, the histological diagnosis of the disease, based mostly on the location, but also in patient with distant metastasis in different location from the organ of origin. And then the biomarkers have defined more and more the individualized treatment for any individual.

So, we went from histology, simple biomarker by immunohistochemistry, and biomarker by NGS, or genomic analysis. As you can imagine over time, we figured out that in fact the disease is very heterogeneous and may change over time in terms of biomarker development and under the pressure of treatment, and can also be different, especially metastatic disease, based on the location of the recurrence. Multiple sites may be different from the original tumor over time, as I mentioned, based on the pressure of the treatment.

So, liquid biopsy is more of a real-time assessment of where the disease biology is, and technology has improved tremendously. Originally, we had only the ability to really examine circulating tumor cells, and this was also a significant challenge when we achieved that now more than 20 years ago, because circulating tumor cells are extremely rare in the peripheral blood of patients with primary metastatic disease. So, it had to be enriched with immunomagnetic separation.

And the first step was actually to enrich and count the cells. And CellSearch was the first technology that got approved. Because when we were able to identify these cells and count these cells, there was a cutoff of five (5) cells both for breast and prostate cancer. This was prognostic, essentially classified the patient with more aggressive disease versus not. Later on, we were able to really establish the ability to individualize treatment based on the biomarkers on CTCs.

Dr. Manish Shah: So, you said that we take some blood from a patient. And using technology, we can identify circulating tumor cells. So, these are cells that are in the blood floating around, and they may represent the tumor. But from a liquid biopsy, I think you were mentioning also that we could look for circulating tumor DNA or cell-free DNA. And that's very different too, right?

Dr. Massimo Cristofanilli: Yes, in the last 10 years, with the improvement in technology, the ability to separate DNA from the patients, the germline DNA from the tumor DNA, and detect a very small amount of tumor DNA, we entered a new era because now the ability to detect small amount of tumor-derived DNA and be able to really classify this tumor based on the specific variant of individual mutations, allele frequency of individual variants, and even fraction of the tumor at different time points, has completely changed the way we address tumor treatment monitoring in the metastatic setting. So, we have the ability to identify CTCs, number and biomarkers. We have the ability to detect cell-free DNA. The two modalities can be complementary.

So, we cannot do, for example, estrogen expression or HER2 expression in the DNA, but we can do amplification, we can do mutations of specific genes including HER2 and ESR mutations in the patient with advanced disease. So clearly, the ability to have a complete characterization of the disease using different liquid biopsy methods.

Dr. Manish Shah: Tumor markers, so, these are proteins like CA-125 or CEA or CA 19-9 that tumors can express and they're secreted and they're in the blood and you can measure them. And then, the higher the level, the more is being secreted by the tumor and it sometimes represents the disease burden.

Now, the more cutting edge is what we're talking about here, which is either circulating tumor cells, so tumor cells that have extravasated from the tumor into the circulation or DNA that may represent the tumor as well, and either of those are now options. But people may come across something called cell-free DNA or circulating tumor DNA. And can you describe the difference if there is any?

Dr. Massimo Cristofanilli: Only a fraction of the cell-free DNA is actually tumor DNA. Sometimes there is contamination by other sources. There's necrotic DNA. We're talking primarily about circulating free tumor DNA. The cell-free DNA, in some cases, they cannot differentiate from germline or abnormal erythropoiesis in some cases cannot differentiate from DNA that is not tumor-derived. But in general, we have the ability to detect, based on technology developed, and be able to filter this DNA that is not derived from the tumor. So, you have specific mutation that are primarily derived from the tumor represented the tumor. In tumors where it is difficult to obtain a tissue biopsy and do a molecular analysis, the reflex test will be the cell-free DNA. And this has been established in lung cancer. It will come pretty soon in breast cancer and in other tumor types. Having a report from a cell-free DNA takes anything between five and seven days. Having a tissue biopsy with NGS or any molecular analysis takes at least two weeks. And of course, it's an invasive procedure.

Dr. Manish Shah: So, this is really exciting. And what you were saying at the beginning is that tumors are heterogeneous. So in the case of metastases, there might be a metastatic lesion in the liver. There might be one in the bone, in the lung, and each of those areas might be somewhat different in terms of some of these biomarkers. And if you are able to do a liquid biopsy, you might be able to get a better sense of the entire tumor because what you're collecting from the blood is not from one tissue, one biopsy, but it integrates all the tumor cells or DNA that leaves the tumor at all those areas and it winds up in the blood. Is that right?

Dr. Massimo Cristofanilli: Correct. I think this is the most exciting aspect of molecular diagnostics. You have shedding from multiple sites. You'll be able to understand exactly how the overall tumor burden and molecular representation of the disease is coming from different sites. We see, for example, in patients with breast cancer, they have soft tissue, liver, and lung, and in hormone receptor-positive, it's not uncommon also to have bone disease. Of course, we don't have an easy access to bone for getting a biopsy. With a liquid biopsy, we can actually understand the contribution of this component from the bone, liver, and lung. And it's also important to differentiate where we will get to the point where the different mutations can predispose to different site of recurrence.

And the liquid biopsy can evolve in a way that tell us not only which mutation is present in the peripheral, but where it's coming from. For example, there are some mutations that are more common in liver versus bone. And we will be able to understand the overall contribution from the shedding, the type of mutations.

Dr. Manish Shah: That's really exciting. So, it sounds like this is potentially very useful, and it will provide more information about the status of the patient's cancer that is underneath the detection of a CAT scan or PET scan. Literally, you can identify individual cells or individual DNA fragments.

You began saying earlier that in breast cancer, the initial circulating tumor cell assays, there was a threshold. And if you had below five, then that was negative, but above that certain threshold, then that was positive and indicated tumor cells. Can you explain why there's a threshold that's not zero? How does that work?

Dr. Massimo Cristofanilli: There is no clear reason why the cutoff of five, actually was able to discriminate patients with more aggressive disease in a shorter survival compared to the patient with less than five. We’ve published a pool analysis just recently. It showed that five remains a very good prognostic and predictive biomarker, meaning that if the patient has been receiving a treatment and there is no change, meaning that the cells do not go below five, the patient has a much shorter survival.

But most importantly, we also showed that there is a continuum from one all the way to five, has worse outcome compared to zero. So clearly, the zero would be the ideal, it depends on the subtype that you have. Anything between one and five seems to be associated with a shorter survival. Five remains the established cutoff that's present also in the FDA clearance and approval back in 2005. So, this is true only for prostate and breast. I think it's been extensively shown in prostate that the response is associated with a drop in CTC. Every time there is this, there is a survival advantage. In colorectal cancer, you may know the cutoff is actually only three and it was never utilized significantly in prospective studies. But the advantage has been also that, in breast and in prostate, we'll be able to assess estrogen receptor, HER2 expression in breast, androgen receptor expression in prostate and RB mutations in prostate as well as ESR mutation most recently in breast. These are mutations associated to the cells, to the DNA within the cells, not cell-free DNA.

Dr. Manish Shah: So, if a patient has a circulating tumor cell count that's less than five, does that mean that the patient will have recurrence, but it'll be delayed, or some of these patients don't have recurrence, so somehow these circulating tumor cells get cleared?

Dr. Massimo Cristofanilli: So, we studied this extensively. There is a tendency to develop metastatic disease in other sites at a much faster rate. So, these patients progressed to visceral metastasis at a faster rate compared to a patient who had less than five. Because this was just prognostic, it was investigated also as a predictive biomarker, meaning that if a patient has more than five CTCs, and an estrogen-positive tumor, can we randomize patients to a more aggressive treatment chemotherapy versus endocrine therapy standard of care for ER positive disease?

This was done from the French investigator in the STIC trial. And it showed that in fact CTC-positive group, the more than five, the ones that have a faster progression, when they're treated with chemotherapy, in spite of being ER positive, do better and proven the progression-free survival, overall survival compared to being treated only with endocrine therapy based on the expression of ER in the tissue. This was proving level one evidence. And in fact, when you have this particular prognostic biomarker, more than five, we will need to intensify your treatment, in this case, with chemotherapy.

Dr. Manish Shah: What you're saying is that CTCs that are greater than five, you have a higher risk of getting visceral metastasis, earlier chance of recurrence and maybe you might benefit from more aggressive therapy. But for patients who are less than five, so maybe not negative, but less than five, can patients clear their CTC without treatment or, does every circulating tumor cell that comes up on the assay, is it actually a cancer cell that could lead to metastasis?

Dr. Massimo Cristofanilli: So, these are epithelial cells that are being demonstrated to be cancer cells. These patients have usually a better and longer response to standard treatments. And again, this has been shown in thousands of patients in multiple studies, prospective or retrospective, there's no resistant to treatment. Eventually, the patient will progress, but it will take a much longer time. That's why there's stratification based on CTCs, even if they don't receive different treatment. The same treatment doesn't work the same way in a patient with more than five CTC or less than five CTCs.

Dr. Manish Shah: So, the CTC count is both prognostic-- people with a higher CTC count have perhaps a more aggressive and a worse survival-- and also predictive. CTCs that are higher than five, they don't benefit the same from the same therapy as lower than five.

Dr. Massimo Cristofanilli: Absolutely, correct.

Dr. Manish Shah: Is the test reliable? If I did a CTC on Monday morning, will I get the same count Wednesday morning?

Dr. Massimo Cristofanilli: Yes. So, this has been studied multiple times of the day to look at the circadian changes, the shedding of the cells, and there was no difference, so multiple times of the day or consecutive days. This was early days when the technology CellSearch was being developed because this obviously was a question that needed to be addressed, put in the application for the FDA.

Dr. Manish Shah: It's a reliable test that's predictive and prognostic. So, based on what you're saying, it seems like everybody should be doing it, right?

Dr. Massimo Cristofanilli: Yeah. This test has been available, as I mentioned, for 20 years. For a period of time, there was an issue with insurance reimbursement. And of course, physicians don't feel that they want to put the patient under the stress of insurance. Right now, it's covered by Medicare and different payers and is available through Menarini, that is the provider. It has a central lab established. You can have CTC enumeration. You can have CTC with biomarker, including PD-L1, HER2. So, it depends on the physician. And if they feel that they want to use it, it's available and it's reimbursed.

Dr. Manish Shah: So, it's available and reimbursed, and it's basically a blood draw. How many tubes? Is it 10 ccs of blood?

Dr. Massimo Cristofanilli: Two tubes of blood. The test is run on a 10 cc. But for this technology, you need to have two tubes of blood.

Dr. Manish Shah: That's really terrific. So then, that's circulating tumor cells. I had a question about the platform. So, you mentioned CellSearch, right? It was one platform. How is that done and what are the differences of different platforms?

Dr. Massimo Cristofanilli: So, CellSearch is immunomagnetic separation, semi-automated. And this being, as I mentioned, the only FDA approved test for prognostic enumeration of epithelial cells. It's a cocktail of biomarkers, essentially a cocktail of cytokeratins and EpCam enrichment method, and you can get the test back in three days.

Now, because of the ability to detect primarily epithelial cells, understanding the metastatic disease may have cells that are no longer epithelial, but mesenchymal. There've been a number of technologies that have been developed without having FDA approval that really use different methods for cells isolation, some by basis on physical microfluidic separation, where the cells are essentially filtered by size to a microfluidic device, and then collected at the end of the process. And these cells can be stained then for the typical biomarker nuclear markers, cytokeratin, other biomarkers. Usually, you see at least the same number of cells, if not more, suggesting in fact that some cells are missed with the CellSearch.

And then, there are filtration systems where there is a much easier process overall. You have the ability to examine and put under the microscope cells, look at morphology of cells and you can theoretically look at also immune cells in the peripheral blood. So, I think the technology available gives it the possibility to expand. These are more for research purposes. If you want to study a more aggressive disease, and you want to understand the evolution of the cells, that's possible. And we have a laboratory where we have several of this technology to evaluate CTC at different stages of the disease.

Dr. Manish Shah: So, CellSearch is the only one that's FDA approved, and it's based on magnetic beads on specific markers, you mentioned EpCam. But then, there are other technologies. So, there was a clinical trial that was presented at ASCO in the plenary session. I believe you were part of that study that really centered on the use of circulating tumor cells as an application. Do you want to talk about that trial? I think that gives us a real-world example of how this could be used.

Dr. Massimo Cristofanilli: You're referring to the cell-free DNA guided intervention.

Dr. Manish Shah: That's SERENA-6. It was cell-free DNA.

Dr. Massimo Cristofanilli: Correct. So essentially, now moving from the circulating tumor cell to cell-free DNA, we know that we have the ability to detect specific mutations that may drive resistance to treatments. And the most common mutation that we have now for which drugs have been approved are founder or truncal mutation in the PIK3CA gene and an acquired mutation, ESR mutation, that appears under depression or endocrine therapy, particularly in patients that have been exposed to aromatase inhibitors.

There was a study called PADA-1 study that showed that if you were to take patients, they had been on a first-line endocrine therapy for metastatic disease with an aromatase inhibitor and a CDK4/6. In that case, it was letrozole and Ibrance, and you monitor their cell-free DNA, over time you see that approximately after six months in a fraction of this patient, you have an ESR mutation that appears. In the design of the study, they plan to essentially stage these patients when they had a mutation and find out if they have a recurrence, they will be treated as a second line treatment. If they had no recurrence, those patients will be randomized to changing the aromatase to fulvestrant and continue CDK4/6 versus continue the same treatment. It would appear that this strategy actually changed the progression-free survival of these patients.

So because of that, we know the Faslodex (fulvestrant), is also not effective in patients with ESR mutation. A group of investigators, and I was involved in the design of this study, decided to design a much larger study where we use a specific drug that is effective in ESR-mutant cells. And this was camizestrant.

So, the SERENA-6 is a two-step study. We had to screen patients that were on AI and CDK4 for more than six months by testing the cell-free DNA every three months. And then, when we detected the cell-free DNA by the cell-free DNA ESR mutations, these patients will be randomized and 315 patients from the original 3,300 patients were found to have an ESR mutation and did not have any evidence of progressive disease. So, they had what we call a molecular progression. So, that was the randomization. This was a placebo control study where the drug, camizestrant, was assigned 1:1 with a continuation of CDK in placebo versus continuation of the aromatase inhibitor, CDK4/6 treatment and the placebo.

There were several stratification factors, but the most important endpoint was the primary endpoint of the progression-free survival by the investigator, but there was pre-planned progression-free survival too after the patient progresses. There was no crossover allowed, and overall survival. This study was presented as a first reading of the progression-free survival, the cutoff for November 28th, 2024 when there were under 25 events. And first of all, when you look at the characteristic of the patients, as I mentioned, it was starting at six months by study design. But the median time for the patient to be randomized was 23 months. And the mutations that were found were the most common that we know in the hotspot mutations. So, the progression-free survival in the patient treated with camizestrant and CDK4/6 with a ESR mutation, no evidence of clinical progression at that time of 16 months versus 9.2 with a hazard ratio of 0.44. So clear significant improvement, and mirroring in a way or improving what we have already seen in patients treated with the PADA-1 study.

Remember, this is the progression-free survival from the moment of randomization. So essentially, the study showed you can extend the benefit of endocrine therapy combination simply by changing the endocrine backbone with camizestrant in patients where the ESR mutation is the only driver of resistance. Of course, we have more data that we have to analyze in terms of the allele frequency of the mutation. As I mentioned, the cell-free DNA has the ability to really mirror the response by imaging studies. We can see what happened to the mutation over time when you switch the drug, particularly the ESR mutation variant, even at the level of the variant. And the most important finding that was obviously quite surprising-- because again, these are patients that have no evidence of clinical recurrence yet-- was the time to deterioration in global health status.

So, these patients maintained their asymptomatic status for much longer, 23 months versus 6.4 months, meaning that this intervention at the molecular level reduced the significant impact that usually metastatic disease has in terms of symptoms in patients with hormone receptor-positive disease. We are analyzing to see if this is a matter of burden of disease, site of recurrence, and so forth.

Dr. Manish Shah: So, the first thing is that you coined a term called molecular progression. I think that's really interesting and it highlights the importance of these liquid biopsies. I know we talked mostly about circulating tumor cells, but the SERENA-6 study, as you pointed out, shifted to the circulating tumor DNA and the mutation identified there. So, molecular progression, for way of definition, it means that there's the occurrence of a mutation that is not seen radiographically that would indicate that there's some activity of the cancer, that demonstrates resistance, that occurs before the development of new metastatic lesions or progression of the metastatic lesions.

Dr. Massimo Cristofanilli: That's correct, yes.

Dr. Manish Shah: So, in the context of having molecular progression, we have a change – in this case, circulating tumor DNA to have this mutation. I think this is really fascinating. By making a change in the hormonal treatment to overcome that mutation, you can extend the time to radiographic recurrence. And you said 16 months versus-- was it nine months?

Dr. Massimo Cristofanilli: Nine months, yes.

Dr. Manish Shah: So, less than a year. But more importantly, the patient's subjective symptoms of the disease were delayed by almost two years, right?

Dr. Massimo Cristofanilli: Yes. I think it's important also, now that you're talking about the molecular recurrence, is not only the fact that you have a new mutation that was not there. We treat the mutation, you delay the symptoms, and you prolong the radiological recurrence.

But this is something that is never done before. So, in a way, changed the thinking of treatment, metastatic, in this case, hormone receptor-positive breast cancer. Most of the guidelines really recommend treatment change, even the combinations. You go from a CDK4/6 combination, for example, to a PI3K combination as a second line based on radiological progression, depression, and mutation.

This is the first time, not only that we treat the molecular progression, but we also change only one drug. We're not changing the combination itself, because the mutation that we see is not due to resistance to a CDK4/6, but due to the resistance to the aromatase inhibitors. So, this is another fascinating aspect of this study.

Dr. Manish Shah: That's a really, really good point. What's the current use of this liquid biopsy?

In terms of the circulating tumor cells that we were talking about at the beginning, you said that they're FDA approved for prostate cancer and breast cancer, and there's a threshold of 5. It's FDA approved for colon cancer, but we don't use it that often. And the higher the number, it's prognostic, meaning the patients will have more aggressive disease and the tumor might return earlier.

In terms of the other aspect of liquid biopsy, which is the circulating tumor DNA, it's a very similar data. So, if the assay is able to detect circulating tumor DNA, meaning DNA mutations in the blood that can only come from the tumor, then it is suggestive that the cancer will have recurrence.

And at least in GI cancers, and it's probably true in other cancers, let's say after surgery, you're in surveillance and you're hoping that the cancer doesn't come back, the identification of the circulating tumor DNA would increase your risk of having the cancer come back to a very high level.

And at this point, unfortunately, we're not really treating based on that value. So, it can cause a lot of stress that this circulating tumor DNA is there. I'm looking for recurrence, I don't find it. I have to do scans, and it can be difficult to handle. But you mentioned here, for the first time, we're basically acting in this area where we have some evidence of progression only at the molecular level. And you can change treatment based on that and you can improve outcomes. Is that fair?

Dr. Massimo Cristofanilli: Yeah. I just want to clarify one thing that you mentioned that's very important and that is, the post-surgical area is most of MRD detection. So, that will be molecular recurrence versus molecular progression. But the point is the same, meaning that if you were to do a test for cell-free DNA on multiple patients over time, prospectively, you see a mutation, nobody treats that mutation in a metastatic setting before the recurrence. So, this would be the setting we're talking about.

In the patients that have surgery, even in breast cancer, now we have evidence that detection of minimal residual disease to cell-free DNA predict for recurrence, but we don't treat that. We just have imaging. And if there is no imaging, we don't know what to do, because there is a period of time where the disease is not detectable for which there is no established intervention. You can certainly anticipate your metastatic first line treatment, but this is not being proved. So, there is no study for that.

So, imagine now a study based on this concept in the early disease for MRD detection, for which we can actually intervene even earlier. So, we can certainly prolong the survival of patients with high-risk disease in the post-surgical treatment. They have a molecular recurrence before the radiological recurrence, but this one is the first step. That's why I'm glad that you connect with that concept, because it's treating the molecular disease evidence only without waiting for the recurrence and prove the concept that in fact, in that case, you can prolong the patient outcome.

Dr. Manish Shah: I'm glad that you clarified that distinction. In colon cancer, there is a study called the DYNAMIC study, where they did a randomized trial. And for stage II colon cancer, there are maybe 25% of patients who have some high-risk features. So, maybe lymphovascular invasion, maybe a large tumor or other features. And patients do receive adjuvant chemotherapy in that context. The trial is randomized to usual care. So, for stage II, maybe 25% of patients would have gotten chemotherapy versus a ctDNA-guided approach where if you were ctDNA-negative, even if you had a high-risk feature at pathology, you wouldn't get treatment. But if you were ctDNA-positive, even without a high-risk feature, you would get treated. And it turns out that you were able to have the same benefit in both arms in terms of the survival, but the patients who are ctDNA-guided, they ended up having actually less chemotherapy. So instead of 25% of patients getting chemotherapy, because it was our best estimate based on high-risk pathologic features, we treated only 17% of patients with chemotherapy. We saved patients from getting chemotherapy when they maybe didn't need it. So, that's another application where potentially if you're ctDNA-negative or maybe liquid biopsy negative would be another way to put it, then maybe you don't need as aggressive treatment in this adjuvant setting.

Dr. Massimo Cristofanilli: Absolutely. I think the example that you brought up that we haven't really investigated in breast is de-escalation of therapy based on the risk, based on the detection of cell-free DNA, as an MRD. Most of the studies in breast cancer are trying to compare an intervention versus another, but I think it's almost unethical to have a control group when you have a positive cell-free DNA. So, we have to get a little bit more pragmatic in that sense. And certainly, de-escalation can be a very good goal in breast cancer. We are giving now CDK4/6 to patients with stage II disease, and in patients with stage III or IV as high risk, maybe the idea of de-escalation instead of giving a drug for two or three years to everyone would be very appealing to patients, especially. And I think this, as a community, of breast oncologists interested in translational research, we should do that.

Dr. Manish Shah: We had a great discussion about circulating tumor cells. On circulating tumor DNA, I just wanted to explain one concept because this is going to come up as well. There are different ways to look for mutations in the blood sample that's collected. One way is called a panel. They look for the most common mutations for that disease, for example. In colon cancer, KRAS mutations are very common. And so, you might devise a strategy where you can look for the most common mutations that occur in the cancer. And then, if you identify them in the DNA that's from the blood, you can say with some high fidelity, that that represents circulating tumor DNA. So, this is what we call a tumor-uninformed analysis.

The other way to do it is actually a tumor-informed analysis. So, you take the patient's tumor, you sequence it, you identify specific areas that you want to track in the blood. And then, using the patient's individual tumor, you can then track those mutations in the blood. And that's very specific for recurrence of that patient's cancer or identification of that patient's cancer in other areas. And so, that might be important as we move forward. But what we're really highlighting is the technology around liquid biopsy. You mentioned all the different technology on circulating tumor cells and the applications of not only looking at the DNA, but also looking at the expression and the receptors and things like that is one aspect. And then, there's technology on circulating tumor DNA, which is on how to assess for those mutations. And I'd like for you to maybe expand a little bit on marrying these two. They're two different things. And we've talked in the past that they should be used synergistically. It's not one or the other, but we should use both.

Dr. Massimo Cristofanilli: That's correct. I mean, just an example, we had a study where we collected and analyzed circulating tumor cells and circulating tumor cell estrogen expression. In the context of prospective randomized study, we did three different arms. For patients that progressed on CDK4/6 versus the combination now, of fulvestrant, palbo in that case, and avelumab and combination with palbo and fulvestrant, the third arm. So, the three groups, they were essentially complementary and equal in terms of efficacy if you don't stratify. When you look at the stratification, and we had also cell-free DNA, the two factors that really differentiated was the fact that you have CTCs and so the patient with fulvestrant did worse and you had the ESR mutation, single-agent fulvestrant did worse. And then, you start to find out that in fact circulating tumor cells in patients with fulvestrant had also less estrogen receptor expression and were associated with the ESR mutation. So, the complementary aspect of this is very important.

I want to go back to an aspect that you were analyzing, is the issue of technology development. Now, the DNA, we've been talking so far about the mutation, single variants, and amplification fusions. We can detect all of that. But now, there is another aspect that is the methylation of DNA. For some of the technology, in particular with the ability to detect small fraction of methylated DNA, and now, moving into the area of screening. You know about colorectal cancer screening and multi-omic screening. With some of this technology in the future, we'll be able to predict which organ we have the methylation signal coming from and direct our imaging.

So, I think it's fascinating that now the blood has the ability to provide all the information that we need, and probably not far the day where we would go from early disease detection associated with the modality that we use right now, according to guidelines, all the way to the disease progression, treatment, primary treatment, monitoring after primary treatment and metastatic disease evolution. So, I think this is an area where our students, our fellows, and our trainees will find themself really in an area of practice that's completely different from what we were training from. And that's important that we train this junior faculty and trainee to the use, and understanding of this technology to be able to apply them in the clinic in the near future.

Dr. Manish Shah: I think it's a really important thing that you highlight. And I think this is true almost exponentially over the last 20 years in oncology that our ability to advance technology is almost exponential. So, the circulating tumor DNA story has been around for about 10 years. And the methylation part of it is, I think, maybe five years. So, it's just accelerating, and it's quite amazing. And you're absolutely right, it's probably not you or I, but other people that we're training or even others that will advance the field even further.

This is a perfect segue to what are you most excited about moving to the future? You know, it feels a little bit like Star Trek where you have some kind of a device, you could just look at something and make a diagnosis. I know we're not there and it's kind of fantasy land, but we're making progress, aren't we?

Dr. Massimo Cristofanilli: The ability to detect very early on cancer can overcome many difficulties in terms of compliance, access to screening. We know that there's never going to be a hundred percent participation in mammographic screening, colorectal screening, and we see tumors in much younger individuals right now. And I think we will need to figure out how to implement this blood screening, even in individuals that have not an obvious risk beside the genetic risk. The genetic risk to me seems to be the first area of intervention. And when you look at the statistics, at the global level, the majority of these patients and mortality come from countries that have low resources. So, we need to make these tests easier to implement, much less expensive. We can certainly change the survival primarily by screening and early disease detection, and not from implementing double or triplet with very expensive drugs. So, I think this is where I see the field is going, where I would like to contribute to. And hopefully, this will be a dream that comes true in the near future.

Dr. Manish Shah: Well, that's terrific. I think if we can use the technology to the benefit of where care is not easy to be received, it could have the biggest impact. Dr. Cristofanilli, thank you so much for your time today.

Dr. Massimo Cristofanilli: Thank you for having me and for bringing up this important topic.

Dr. Manish Shah: Well, that's all for now, folks. You can download, subscribe, rate, and review CancerCast on Apple Podcasts, Spotify, YouTube, or online at weillcornell.org. We also encourage you to write to us at cancercast@med.cornell.edu with questions, comments, and topics you'd like to hear us cover in the future. That's it for CancerCast, conversations about new developments in medicine, cancer care, and research. I'm Dr. Manish Shah. Thanks for listening.

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