Fluorescent Findings: Making Sentinel Node Mapping Accessible in Vet Med

A glow under blue light might be the difference between guessing and knowing where cancer has spread. We sit down with Drs. Elizabeth Maxwell and Veronica Perez to unpack a practical, low-cost approach to sentinel lymph node mapping in dogs using fluorescein sodium, a compound many veterinarians already recognize from everyday clinical use. Our focus stays on one big goal: expanding access to accurate cancer staging in veterinary oncology without requiring advanced imaging, specialized near-infrared camera systems, or a referral-only workflow. 

We walk through the real surgical details: intradermal injections around the tumor, quick massage for lymphatic uptake, then watching the lymphatic channels appear in real time with handheld lights and blue light filtering glasses. Elizabeth and Veronica share why simplicity matters for adoption in general practice, what they learned about black light versus blue light clarity, and why “I can see it with my eyes” can reduce friction in the operating room. 

Then we get into the stakes. In their pilot study of six client-owned dogs, the team identified at least one sentinel lymph node in every case, with rapid visualization after injection. Histopathology underscores the clinical value: metastatic mast cell disease showed up in sentinel nodes, including early nodal metastasis that palpation alone could miss, and even deeper second-tier nodes in some dogs. We also cover key limitations, including small sample size, qualitative assessment, and the need for head-to-head trials against standards like indocyanine green near-infrared fluorescence to define sensitivity, specificity, and false negative rates. 

If you care about affordable veterinary cancer care, better surgical decision making, and practical tools that can move beyond specialty centers, this conversation is for you. Subscribe, share with a colleague, and leave a rating or review on Apple Podcasts or wherever you listen, then tell us what would help you adopt sentinel lymph node mapping in your own clinic.

JAVMA article: https://doi.org/10.2460/

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Transcript

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Welcome And Research Focus

Lisa Fortier 0:35

Welcome to Epic Award-winning Veterinary Vertex, the AVMA Journal's podcast where we delve into behind-the-scenes looks with manuscript authors. I'm editor-in-chief Lisa Fortier, joined by Associate Editor Sarah Wright. Today we're discussing expanding access to cancer care with Elizabeth Maxwell and Veronica Perez.

Sarah Wright 0:54

Thank you for joining us, Elizabeth and Veronica. Thank you for having us. Yeah, thank you for having us.

Accidental Discovery Of Fluorescein

Lisa Fortier 0:59

All right, Elizabeth, let's start with you. What motivated your team to investigate fluorescein sodium for sentinel lymph node mapping in dogs?

SPEAKER_01 1:07

Uh so, like with all great discoveries, sometimes they happen by accident, right? So I was actually working with a novel nanoparticle for sentinel lymph node mapping, and they're supposed to fluoresce under near-infrared imaging systems, but we couldn't get them to fluoresce at that wavelength, but we were able to get them to fluoresce under black light. And a kind of light bulb sort of went off in my head, like, wow, wouldn't that make sentinel lymph node mapping so much more accessible if we could just use a black light? So then I went down this like rabbit hole looking for substances or compounds that we could essentially inject that would, you know, glow in the dark or glow under black light. And that's when I came across the commercially available fluorescene. Um and, you know, it's commonly used in ophthalmology for retinal angiography in humans. And we're of course familiar with using it for corneal staining. And it has been investigated as setinal lymph none mapping agent in human oncology, particularly with breast cancer patients. And so in my research, I saw that there was one canine cadaveric study available. And so, with all that information, we had enough to start developing a project investigating its use for sentinel lymph node mapping in clinical cases.

Sarah Wright 2:24

Very cool. I always love to hear when things just like happen by accident, and then we actually get to start implementing them. So thank you for

Why Mapping Is Hard To Access

Sarah Wright 2:30

sharing that. Veronica, what are the current challenges associated with sentinel lymph none mapping in veterinary oncology?

SPEAKER_03 2:37

Yeah, the the challenge isn't that we don't have ways to perform sentinel lymphomping. We do. I think the challenge is making those techniques practical and accessible for everyday clinical use. And so right now, the standard techniques rely on advanced imaging like CT lymphography, specialized near infrared camera systems. And I think this creates kind of like a triple thread of barriers for the average practitioner. You have the need for special specialized equipment, a high cost, the need for specialized training sometimes. And so these mapping techniques aren't things that you can just pick up and do tomorrow. They require significant extra education, technical mastery. And sometimes you even need a specialized team to execute them. And so, because of these hurdles, the procedures are essentially locked behind the walls of a specialty referral center or an academic institution. And the high cost isn't just a hurdle for the practitioner who faces the massive upfront expense of acquiring the equipment, maintaining it over time. It directly hits the patients and their families too, because the tools are locked away and the families have to face this heavy financial burden of referral fees, specialized consultation costs, the cost of advanced imaging. And so this often forces owners to make heartbreaking compromises on care due to financial or even geographical limitations. And that's kind of really what motivated our interest in looking at fluorescence too.

Lisa Fortier 4:08

Yeah, it must give them a lot of anxiety too. Like they're with their trusted doctor, and now you're going to ship them someplace else. So it's really great. Uh, in the whole spectrum of care, the more we can keep with the home team, I think that's best. I agree. Veronica, can you briefly describe how fluoresceine-guided mapping procedures were performed in

Step By Step Mapping In Surgery

Lisa Fortier 4:26

your study?

SPEAKER_03 4:26

Yeah. The procedure itself was relatively straightforward and it kind of integrates seamlessly into your standard surgical prep. We administer about two to three uh mils of a one in 120 uh dilution of 10% fluorescence, and we split that volume into intradermal injections around the tumor in a four-quadrant matter. Um we then gently massage the area for at least about a minute to facilitate lymphatic update uptake. Um and then from there, we monitored the surgical field using two different handheld devices. One was a blue light, the other was a black light. And then we put on some um uh blue filtering, blue light filtering glasses. And this kind of allowed us to watch the fluorescene travel through the lymphatic vessels in real time. And then as those pathways became visible, we would follow them to identify and isolate the sentinel lymph node, and then the node would be surgically excise and then submitted for pathology.

Sarah Wright 5:28

Yeah, it's fascinating. Elizabeth, what made fluoresce sodium an attractive candidate for this application?

SPEAKER_01 5:35

So, what initially drew us to want to investigate fluorescein was the simplicity of it. It's you know used safely in human medicine for decades. It's inexpensive, widely available, and produces a very bright fluorescent signal when exposed to the black or blue light. Um, you know, as Veronica said, the current sentinel lymph node mapping tech techniques often require specialized imaging systems, which can cost tens of thousands of dollars and are typically only found in referral hospitals. And we wanted to explore whether, you know, a readily available compound and a simple light source could provide a similar clinical utility. And I mean, you can just see it with your eyes, right? Like there isn't that added element of looking back and forth between a monitor and the patient or coordinating what you see on the screen with what you're doing surgically. That's very cool.

Lisa Fortier 6:31

Veronica, for the listener and for our veterinary profession, what are the most important findings from your study regarding this lymph node identification?

Speed And Success Of Identification

SPEAKER_03 6:40

So I think the most exciting takeaway is that the technique is effective and fast. We achieved 100% success rate. Um, we identified at least one sentinel lymph node in all six dogs. Um, we also visualized the actual lymphatic tract that led to those nodes in about 83% of our cases. And I think what makes this really practical for a clinical um, for a busy clinic, is the timeline. Your lymphatic tract, our lymphatic tracts lit up in a meantime of about 6.77 minutes. Um, and the actual sentinel node were fluorescent about eight minutes post-injection. Um and we found that using the standard blue light with the filtering glasses subjectively gave us a much clearer, sharper view of the pathway than the black light.

Sarah Wright 7:32

Sometimes when we're performing research, we find things that surprise us, things that we don't expect. Elizabeth, were any of the results in this study unexpected?

SPEAKER_01 7:40

So we did find that sometimes we needed to use a larger volume than expected for more distant lymph nodes or for larger tumors. So while one mil is often sufficient when we're sentinel lymph node mapping with ICG, sometimes with the fluorescein, we did have to go up to two mils or or a little more than that with the fluorescene solution. And I'd say we weren't really sure what the difference was going to be between using the blue light or the black light. So it was surprising to see that although the fluorescein solution fluoresces really nicely under the black light, once you injected it into the skin, it became challenging to see. On the other hand, the blue light isn't easy to see the tract until you put the blue light blocking glasses on. And then once you put the glasses on, you see it very, very clearly.

Lisa Fortier 8:32

Veronica,

Surprises With Blue Versus Black Light

Lisa Fortier 8:33

what about the histopath findings? What did they reveal about the clinical value of identifying sentinel lymph nodes? Was there anything unique with your study compared to previously reported literature?

SPEAKER_03 8:44

Yeah, the histopath really highlighted why we cannot rely on colpatient alone for staging. Um, out of the six dogs, four had confirmed metastatic mast cell disease in their sentinel lymph nodes. And two of those were early nodal metastasis or HN2, and two were overt metastasis or HN3. Interestingly, we also caught some downstream metastasis. In two dogs, we identified second-tier nodes, particularly the retropharyngeal lymph node. Um, one of those, you know, hidden deeper nodes that were those nodes were actually harboring um HN2 mast cell metastasis. And I think, you know, without this technique, guard guiding our excision, those metastatic nodes could have easily been left behind and it could have altered the patient's prognosis.

Sarah Wright 9:34

Yeah,

Metastasis Findings On Histopath

Sarah Wright 9:35

well, it's right. Elizabeth, what did you learn about the safety and practicality of this technique in the clinical setting?

SPEAKER_01 9:42

So we did not observe any adverse events associated with the fluorescene administration, but it is only six dogs, so uh larger studies would uh need to be performed to evaluate safety. Uh and the procedure added very little complexity to the surgery. Uh equipment requirements were minimal, so you just your flashlight and your you know blue light blocking glasses, and then the visualization occurs in real time. So, from a clinician's perspective, that's really important because any new technique has to fit into busy surgical schedule to be widely adopted.

Safety Practicality And Owner Impact

Lisa Fortier 10:16

Uh we talked about the histopath, but could this technique influence staging and treatment planning for dogs with cancer?

SPEAKER_03 10:22

Yeah. So I think from an owner's perspective, um, this technique is, I think, a major win for expanding access to high quality cancer care. Right now, um, the gold standard is going to be, you know, referring the patient to a specialty oncology center for specialized imaging, um, maybe specialized like intra-op techniques. And then, and you know, for many pet parents, that means, again, a mass, massive financial hurdle taking time off work or driving hours to a university or a referral hospital. And so I think by utilizing a low-cost, ready, readily available agent like fluorescence sodium, along with the standard, you know, blue light equipment that you can purchase really anywhere, including Amazon, um, your general practitioner can accurately stage a tumor right in their own local community clinic for the owner. And, you know, I think this changes everything because instead of facing a costly referral just to find out if the cancer has spread, they can get a somewhat immediate, precise answer from the vet they already know and trust. And it empowers them to make a highly informed decision about treatment plans or surgery without the, you know, added logistical stress and expense of having to go to that referral center. Um because it I think it's truly putting advanced oncology mapping into a realistic, affordable spectrum of care for the everyday family.

Lisa Fortier 11:47

Yeah, it's very important. So important. Um, Elizabeth, are there any specific patients or tumor types that are most likely to benefit from this approach?

SPEAKER_01 11:56

So patients with tumors that have a high risk of lymphatic metastasis are likely to benefit the most. In dogs, that includes your mast cell tumors, melanomas, and carcinomas. We know that the anatomically closest lymph node is not always a true draining or sentinel node. So mapping is going to improve staging accuracy and help guide the surgical decision making. So, really, any patient in which lymph node status influences prognosis or treatment planning could potentially benefit.

Limits Of The Pilot Study

Sarah Wright 12:26

Veronica, what are the primary limitations of your study?

SPEAKER_03 12:29

It's a pilot study, right? So I think our biggest limitation is scale. Uh, we only looked at a small cohort of six client-owned dogs. They had a mix of different cutaneous and subcutaneous tumor types. And I think because of that, we can't really run robust statistical analysis or make broad or broadly generalize our findings to all canine cancers. And I think our assessment of the fluorescence also was, you know, purely qualitative and subjective, meaning, you know, we judged complete versus partial uptake by using our eyes and not necessarily using something like a special specialized digital software. And, you know, lastly, but no less important, is we didn't perform a direct head-to-head comparison of these dogs against a traditional mapping agent like uh NERF with ICG.

Lisa Fortier 13:18

Veronica, what additional studies are you going to perform that might that won't take this to the same level of complexity and cost and all the other things that are available for the other types of mapping?

SPEAKER_03 13:30

Yeah, so I think moving forward, we need larger controlled perspective studies that kind of stratify the dogs by specific tumor types and anatomical locations. We also want to introduce a standardized, you know, quantitative tool to measure our fluorescence intensity so we can pass the subjective visual assessment. I think most importantly, we need to have those head-to-head diagnostic trials where we're comparing fluoresce against um ICG and near near infrared fluorescence, um, because those are our standards of care currently. And I think that will allow us to definitively calculate like its true sensitivity specificity, you know, or false negative rates and veterinary oncology.

Next Studies And Future Of Mapping

Lisa Fortier 14:11

Yeah, love it. Are you gonna do that study? We're working on it. Awesome.

Sarah Wright 14:18

Happy to hear that. Hopefully get to see it. Uh Elizabeth, how do you envision sentinel lymph node mapping evolving in veterinary practice over the next several years?

SPEAKER_01 14:28

So I think we're approaching a point where removing the regional lymph node is a routine part of cancer surgery in specialty practice, much like obtaining tumor margins or submitting tissues for histopathology. And as we continue to learn that the anatomically closest lymph node is is often not the true draining lymph node, accurately identifying the sentinel lymph node will become increasingly important for staging and treatment planning. But the key to widespread adoption for sentinel lymph node mapping in the private practice setting will be accessibility. And right now, many mapping techniques require specialized equipment, so that's going to limit their use to referral centers. So as more affordable practical options become available, I would envision the sentinel lymph node mapping, you know, moving beyond specialty hospitals and into general practice. And ultimately, my hope is that any veterinarian performing oncologic surgery, whether in specialty center or primary care setting, will have access to a reliable mapping technique and view sentinel lymph node mapping or sentinel lymph node identification as a standard component of cancer surgery rather than an advanced procedure. So that shift has the potential to improve staging and accuracy and cancer care for a much larger population and veterinary patients.

Clinician Takeaways And Closing

Lisa Fortier 15:43

Yeah, really well said. And so, Veronica, for the listener who might be thinking about adopting this, what's an important takeaway for any of those clinicians considering adopting this technique? And then after Veronica, maybe Elizabeth, if you have anything else to add.

SPEAKER_03 16:10

Through our study, we didn't have any adverse events or hypersensitivity reactions in any of the dogs. From a practical standpoint, it's important to know that, you know, while we successfully localized the sentinel lymph node in all of our cases, a visible track or pathway was present in only about 83% of our cases. And so this means that while the dye gives you an incredible real-time visual map in most patients, it doesn't completely replace clinical judgment. And so in cases where a distinct tract doesn't light up, you still rely on standard regional drainage patterns to guide your node dissection. Um and hopefully, once you dissect down to your node, the node will be fluoresced. Um it's I think it's a highly um reliable intra-op tool so far, and it provides immediate surgical confidence without having a very steep learning curve.

SPEAKER_01 17:08

Yeah, and I'd say the most um one of the most important takeaways is that cost should not be a barrier to providing advanced oncologic care. And this technique could offer veterinarians a simple, affordable, and accessible way to perform setinal lymph node mapping, particularly for patients seen in general practice where advanced imaging equipment is not available. And for specialty surgeons, fluorescene could serve as a lower cost alternative, a complementary technique or even a useful tool in settings where advanced imaging equipment is not available. But ultimately, the goal is not to replace near infrared imaging, but to make cancer staging uh available to more patients. I love that. What a great takeaway.

Sarah Wright 17:52

Well, Elizabeth and Veronica, thank you so much for joining us and for sharing this important study to you with JAFMA. Thank you for having us.

SPEAKER_03 17:59

Yeah, thank you for having us.

Sarah Wright 18:00

For our listeners and viewers, you can read Elizabeth and Veronica's article on JAFMA. I'm Sarah Wright with Lisa Fordier. Be sure to tune in next week for another episode of Veterinary Vertex. And don't forget to leave us a rating or review and Apple Podcasts or wherever you listen.