Cathy Eng, MD, FACP, FASCO

Cathy Eng, MD, FACO, FASCO, the David H. Johnson chair in Surgical and Medical Oncology, co-leader of the Gastrointestinal Cancer Research Program, professor of Medicine (Hematology and Oncology), co-Director of GI Oncology, vice-chair of SWOG GI Committee, and the director of the VICC Young Adult Cancers Initiative at Vanderbilt-Ingram Cancer Center discusses how biomarkers are being explored to aid the treatment of anal cancers.

Biomarkers in the anal cancer space is an area of active research, explains Eng. The biomarker with the most research currently is PD-L1 expression, which first showed promise in other solid tumors as a predictor of response to immune checkpoints inhibitors. More research is needed in the field.

 The role of biomarkers is largely exploratory. The 1 biomarker that's been most heavily explored is obviously PD-L1 expression, which has been explored in multiple other malignancies where immune checkpoint inhibitors are being considered. For anal carcinoma, keeping in mind this is a rare cancer, the original data regarding pembrolizumab [Keytruda], noted that there was still benefit in patients that were PD-L1 overexpresses versus those that were not. Then, in our original trial looking at nivolumab [Opdivo] in the refractory setting, a smaller study, but also we were not selective and did not require PD-L1 expression to participate in the trial, we still had patients that were also responders. Once again, the numbers are much smaller, because we're a rare patient population. We hope to derive, hopefully more data in the future, moving forward with looking at immune checkpoint inhibition.

 I do not believe biomarkers are being utilized fully in the space because I think, in large part, funding has been an issue. There has been data that was created or attempted to be created from the INTERACT trial, which I also participated in. And that was basically limited to select sites because of limited funding. Same story, when we wrote up our ETCTN trial, we had limited funding as well. And only we were able to basically evaluate samples from patients that we treated at MD Anderson Cancer Center. Ironically enough, currently in our phase 2 randomized study, MCI 9673 part b, although we actually have funding this time around, I think a lot of patients are more interested in circulating tumor DNA, just because of the convenience, rather than providing a tissue sample even though we actually were able to obtain funding this time. So, I'm a little concerned although we don't have the final numbers. I'm a little concerned about the number of tissue specimens we were hoping to achieve from our randomized phase 2 study. So, I think moving forward, based upon all the phase 1-3 trials that have been created, I hope we will be able to derive more information and I'm hoping that similar information will be derived from all these individual studies so that we can learn something cumulatively.

Videos

Cathy Eng, MD, FACO, FASCO, discusses how biomarkers are being explored to aid the treatment of anal cancers.








The Role of Biomarker Testing in Anal Cancer

 fusion resistance to larotrectinib and also specifically for the NTRK inhibitors, and that is 

 G595R. There is a drug specific to that called LOXO-195, which is approved to be utilized in that setting.

I would say that basically this literature regarding the 

fusion and its significance is important across all malignancies. Although I focus specifically on colorectal carcinoma, the 

 fusion is more common in other malignancies, such as papillary thyroid carcinoma, salivary gland carcinoma, and more common in pediatric tumors.

It is advantageous for other malignancies, not necessarily colorectal carcinoma, but it appears to have a role, specifically even higher in the MSI [microsatellite instability]-high positive colorectal cancer tumors. And the fact that it's an oral agent with such significant response.

Once again, if the patient tolerates it well and given that there are several patients who we treat, on a day-to-day basis, with refractory colorectal carcinoma that are surgically unresectable, if they're 

positive, obviously this is another drug that would be advantageous in the armamentarium to treat our metastatic colorectal cancer patients.

Case: A 68-Year-Old Woman With Metastatic 

A 68-year-old woman presented with a 3-month history of intermittent abdominal pain, and alternating constipation/diarrhea

PMH/SH: hypertension and hypercholesterolemia, medically managed; colonoscopy at age 50 was unremarkable; never smoker; no family history of cancer

PE: abdomen tender on deep palpation in the right lower quadrant

Labs: Hb 11.9, Hct 32%, MCV 75 fL, CEA 12.8 ng/mL

Chest/abdominal/pelvic CT showed a 5-cm right sided bowl mass and multiple hepatic lesions, and regional lymphadenopathy

Colonoscopy revealed a 5-cm mass in the ascending colon, biopsy was taken

Pathology: grade 3 poorly differentiated adenocarcinoma, with invasion of the submucosa

Biomarkers: KRAS-wt, NRAS-wt, BRAF-, NTRK+; MSI-H

NTRK Fusion–Positive Colon Cancer: Final Thoughts

In regard to the dosing for larotrectinib, the standard dosing is 100 mg bid [twice a day]. Once again, it comes in an oral and a liquid form. And obviously that’s advantageous for some of our patients, not necessarily just colorectal cancer patients, keeping in mind that 

There were some grade 3 toxicities, but no grade 4 or 5 toxicities.

Of the toxicity seen with larotrectinib, for grade 3 toxicities, they were fairly mild, one being anemia. That was in about 14% of patients. I would say for any oral agent, obviously you have to be very mindful of how well the patient is adhering with taking the medications as directed.

You still have to follow the patients regardless of the fact that it is more convenient for them to take an oral agent. My tendency for any oral agent is to follow the patients at least every 2 weeks for the first month. Then, give or take, maybe considering that as well for the second month. And then after that, I may cut it back to just once a month. That is my tendency with all patients on oral agents, not just the NTRK inhibitors.

NTRK-Targeted Therapy in Colon Cancer: Dosing and Management

 Regarding the mechanism of action for larotrectinib, as well as entrectinib, which is one of the other NTRK inhibitors, larotrectinib is a pan-TRK inhibitor that is an oral agent and also comes in a liquid form. It's an ATP [adenosine triphosphate]-competitive binder. In comparison, entrectinib is not only a pan-TRK inhibitor, but also impacts 

. They are a little bit different; larotrectinib is specifically an NTRKinhibitor.

In regard to the efficacy of larotrectinib, the response rate is quite impressive. The response rate, the last time that I reviewed the data, was 81%, with a significant number of patients in PR [partial response] and CR [complete response]. In regard to toxicities, there were no significant, major toxicities that we would consider a concern, especially for grade 3 and 4.

In the other studies however, for entrectinib, there was some grade 3/4 toxicity in regard to fatigue that was noted and some other nonspecific toxicities, such as dysgeusia.

In regard to the duration of response, what I've gathered from the data is that there is significant duration of response for the majority of patients. This obviously can be pivotal in patients who have had refractory metastatic disease.

This patient is unique in the sense that she is treatment naïve. However, the majority of patients with surgically unresectable disease will need to continue chemotherapy or some type of treatment indefinitely. It's imperative from my perspective that all patients, number 1, should be tested for MSI [microsatellite instability] high, but also for the 

 fusion because this provides them a different, unique opportunity for the continuum of care rather than just a standard systemic chemotherapy.

In that aspect, I would say that this class of drugs is really pivotal, especially for our patients in the refractory population who have been through multiple prior lines of therapy.

NTRK-Targeted Therapy for Patients With Colon Cancer

The treatment options for this newly diagnosed patient with surgically unresectable disease based upon the fact that she reportedly has multiple liver metastasis, if her performance status is quite good, which it appears to be, with an ECOG [Eastern Cooperative Oncology Group] performance status of 1, obviously your treatment options may be to consider standard chemotherapy up front.

Secondly, you can consider immunotherapy, which now has been not only considered in the refractory setting of patients who have received at least 1 prior therapy, but as many of you know, it is already approved as per the NCCN [National Comprehensive Cancer Network] guidelines for patients who may not tolerate chemotherapy well. There are a lot of data, not only looking at single agent, but also doublet therapy with nivolumab and ipilimumab.

Then obviously the third option in this setting, which would be important if she tests positive for 

 fusion, is to consider the role of one of the NTRK inhibitors.

Patients who are MSI [microsatellite instability] high are more likely to test positive for the 

So although is it going to be less than 1% of all patients with colorectal cancer who will have an 

 fusion, it’s reportedly between 25% and 30% of MSI-high patients who are 

In the setting of this patient, when I would want to consider utilizing larotrectinib, my preference would be to consider immunotherapy up front, and utilize one of the NTRK inhibitors at progression of disease. That would be my preference at this time, and that is because most of the literature regarding immunotherapy has a little bit more history and is longer-standing with greater median follow-up.

Are there any circumstances in which I would not want to provide targeted therapy in the setting of this driver mutation? I think based upon this case and based upon the literature that exists, my preference would not be to not pursue targeted therapy in this setting. I think is the most appropriate setting, in this patient who has an MSI-high tumor as well as an

Treatment Options for NTRK Fusion–Positive mCRC

The preferred methods for testing for the 

 fusion, I think most of us nowadays are utilizing next-generation sequencing [NGS]. I think that's commonly being done across all, not only academic institutions, but community practices as well. I think it is more important that you also learn more about the companies that you're working with, where you're sending out the specimens, in regard to your NGS panels.

 fusion. The majority of NGS panels nowadays, or the evaluation for the specimens, includes the use of RNA sequencing, which will then have increased sensitivity and specificity.

In regard to testing for the platforms that you're looking at with the 

 fusion, once again, you really need to evaluate where you're sending out your specimens. You need to ensure that they are actually able to evaluate

The majority of companies that are looking for these 

fusions are able to capture and track 1, 2, and 3, which are the forms that we were looking for. But more importantly, once again it's extremely significant to make sure that all patients are tested for microsatellite instability [MSI].

That is recommended in all patients regardless of whether you're considering an NTRK inhibitor. As everybody knows, there is a significant role for immunotherapy in our patient population that has been determined to be MSI high. And then obviously, more importantly for the younger patients, those patients should be evaluated by a genetics group.

Cathy Eng, MD, FACP, FASCO | Authors

Articles

The Role of Biomarker Testing in Anal Cancer

NTRK Fusion–Positive Colon Cancer: Final Thoughts

NTRK-Targeted Therapy in Colon Cancer: Dosing and Management

NTRK-Targeted Therapy for Patients With Colon Cancer

Treatment Options for NTRK Fusion–Positive mCRC

Testing for NTRK Fusion–Positive Metastatic Colon Cancer